Class 9 Science Chapter 8 MCQ: A Journey through States of Water — 30 Questions with Answers

The CBSE Board has redesigned the Class 9 Science exam to emphasize higher-order thinking skills. MCQs are no longer 'fill one word' questions; they now test conceptual understanding, real-world application, and reasoning. In Chapter 8, the board expects students to not just memorize definitions but to explain why water changes state at specific temperatures, how the water cycle sustains life, and why water conservation is critical in arid regions. MCQs force precision: you cannot half-answer a multiple-choice question. You either know the correct concept or you don't. This format also trains you for competitive exams like KVPY, NTSE, and JEE Main, where MCQs with single correct answers dominate. Additionally, the new CBSE pattern includes assertion-reason type MCQs, where you must evaluate both a statement AND its reasoning. These require deeper conceptual rooting than traditional 'one-liner' questions. By practicing 30 graded MCQs—from easy to hard—you build pattern recognition skills that transfer directly to exam performance. You'll learn to spot trap options designed to catch students who memorized facts without understanding. This is why targeted MCQ practice, rather than passive textbook reading, yields the highest score improvement in CBSE Class 9 Science.

**Q1.** Which of the following is NOT a state of matter? (A) Solid (B) Liquid (C) Gas (D) Plasma **Answer:** (D) Plasma **Reason:** Plasma is a fourth state of matter; the NCERT Chapter 8 focuses on solid, liquid, and gas only. **Q2.** Ice is a _____ state of water. (A) gaseous (B) liquid (C) solid (D) vapour **Answer:** (C) solid **Reason:** Ice is water in its crystalline solid form; molecules are tightly packed in a fixed structure. **Q3.** The process by which a solid changes directly into gas without becoming liquid is called: (A) Melting (B) Evaporation (C) Sublimation (D) Condensation **Answer:** (C) Sublimation **Reason:** Dry ice (solid CO₂) undergoes sublimation; this process skips the liquid phase. **Q4.** Boiling occurs when the vapour pressure of a liquid equals: (A) Atmospheric pressure (B) Its density (C) Its molecular weight (D) Its specific heat **Answer:** (A) Atmospheric pressure **Reason:** At boiling point, molecules escape the liquid in bubbles throughout the liquid, not just at the surface. **Q5.** The melting point of ice at standard pressure is: (A) 0°C (B) 100°C (C) −40°C (D) 50°C **Answer:** (A) 0°C **Reason:** NCERT defines 0°C as the standard melting point of ice under 1 atm pressure. **Q6.** When water vapour condenses, it becomes: (A) Ice (B) Liquid water (C) Dry ice (D) Steam **Answer:** (B) Liquid water **Reason:** Condensation is the reverse of evaporation; gas transforms into liquid when cooled. **Q7.** Evaporation is a _____ process. (A) Slow, temperature-dependent (B) Instantaneous (C) Pressure-independent (D) Only occurs at 100°C **Answer:** (A) Slow, temperature-dependent **Reason:** Evaporation occurs at any temperature, faster at higher temperatures; it's continuous at the liquid surface. **Q8.** Which process is OPPOSITE to melting? (A) Boiling (B) Freezing (C) Evaporation (D) Sublimation **Answer:** (B) Freezing **Reason:** Melting converts solid to liquid; freezing converts liquid back to solid at the same temperature. **Q9.** Water exists as a solid below: (A) 0°C (B) 100°C (C) 50°C (D) −50°C **Answer:** (A) 0°C **Reason:** At temperatures below 0°C under standard pressure, water molecules lack energy to overcome the solid lattice structure. **Q10.** The boiling point of water at standard atmospheric pressure is: (A) 50°C (B) 100°C (C) 150°C (D) 0°C **Answer:** (B) 100°C **Reason:** NCERT standard: water boils at 100°C under 1 atm pressure; this is a fundamental constant in the chapter.

**Q11.** In the water cycle, water evaporates from oceans, lakes, and rivers. This water vapour rises and cools. What happens next? (A) It freezes into snow (B) It condenses into clouds (C) It sublimates (D) It dissolves in air **Answer:** (B) It condenses into clouds **Reason:** As vapour rises and temperature drops in the atmosphere, condensation occurs around dust particles, forming clouds. **Q12.** If the boiling point of a liquid increases with increasing atmospheric pressure, which of the following statements is TRUE? (A) The liquid is boiling at a lower temperature (B) Fewer molecules escape as vapour (C) More energy is required for molecules to overcome atmospheric pressure (D) The liquid is not pure **Answer:** (C) More energy is required for molecules to overcome atmospheric pressure **Reason:** Higher atmospheric pressure pushes down on the liquid surface, requiring more molecular kinetic energy (higher temperature) to form escaping vapour bubbles. **Q13.** Which of the following is an example of SUBLIMATION in everyday life? (A) Melting ice cream in summer (B) Naphthalene balls disappearing from a wardrobe without leaving liquid (C) Water boiling in a kettle (D) Rain falling from clouds **Answer:** (B) Naphthalene balls disappearing from a wardrobe without leaving liquid **Reason:** Naphthalene undergoes direct conversion from solid to gas, leaving no liquid phase—a classic example in NCERT. **Q14.** During the water cycle, transpiration refers to: (A) Water evaporating from soil (B) Water released by plants into the atmosphere (C) Water absorbed by plant roots (D) Water condensing in the atmosphere **Answer:** (B) Water released by plants into the atmosphere **Reason:** Transpiration is water vapor released from plant leaves; combined with evaporation, it's called evapotranspiration in the hydrological cycle. **Q15.** If ice cubes are placed in a container and left at room temperature (25°C), which phase transition occurs? (A) Freezing (B) Condensation (C) Melting (D) Sublimation **Answer:** (C) Melting **Reason:** Ice absorbs heat at 25°C, causing molecules to gain kinetic energy and break free from the solid lattice, forming liquid water. **Q16.** The latent heat of vaporization for water is the energy required to: (A) Raise the temperature of water by 1°C (B) Convert 1 kg of liquid water to vapour at constant temperature (C) Melt ice at 0°C (D) Freeze water at 0°C **Answer:** (B) Convert 1 kg of liquid water to vapour at constant temperature **Reason:** Latent heat breaks intermolecular bonds; during vaporization, all heat energy goes into phase change, not temperature rise. **Q17.** Why does moisture appear on the outside of a cold water glass on a hot day? (A) Water leaks through the glass (B) Water vapour in the air condenses on the cold glass surface (C) Ice forms on the glass (D) The glass sweats due to osmosis **Answer:** (B) Water vapour in the air condenses on the cold glass surface **Reason:** The cold glass surface cools nearby air below its dew point, causing atmospheric water vapour to condense as liquid droplets. **Q18.** In high mountains, water boils at a temperature lower than 100°C. This is because: (A) Air is cooler (B) Atmospheric pressure is lower at higher altitudes (C) Ice melts faster (D) Water is purer **Answer:** (B) Atmospheric pressure is lower at higher altitudes **Reason:** Lower atmospheric pressure means molecules need less kinetic energy (lower temperature) to escape the liquid surface, so boiling occurs at lower temperatures. **Q19.** Which of the following correctly describes the relationship between evaporation and condensation? (A) Evaporation absorbs heat; condensation releases heat (B) Both absorb heat (C) Both release heat (D) Evaporation releases heat; condensation absorbs heat **Answer:** (A) Evaporation absorbs heat; condensation releases heat **Reason:** Evaporation is endothermic (absorbs latent heat); condensation is exothermic (releases latent heat)—they are reverse processes with opposite energy flows. **Q20.** Water conservation is critical because: (A) The total amount of water on Earth is decreasing (B) Only 3% of Earth's water is freshwater, and most is locked in ice caps and groundwater (C) Boiling water removes all impurities (D) Evaporation prevents water recycling **Answer:** (B) Only 3% of Earth's water is freshwater, and most is locked in ice caps and groundwater **Reason:** NCERT Chapter 8 emphasizes that accessible freshwater is extremely limited; wasteful usage threatens ecosystems and human populations.

**Q21.** **Assertion:** Boiling and evaporation both convert liquid water to gas, so they are identical processes. **Reason:** Both processes occur when molecules gain sufficient kinetic energy to escape the liquid. (A) Both assertion and reason are true; reason correctly explains assertion (B) Both assertion and reason are true; reason does NOT explain assertion (C) Assertion is true; reason is false (D) Assertion is false; reason is true **Answer:** (D) Assertion is false; reason is true **Reason:** Boiling is rapid (bubbles throughout liquid, at fixed temperature), while evaporation is slow (surface only, at any temperature). The reason is true but doesn't justify the false assertion. **Q22.** **Assertion:** When ice melts at 0°C, the temperature of the system remains constant until all ice has melted. **Reason:** All heat energy supplied during melting goes into breaking intermolecular bonds (latent heat), not increasing molecular motion (temperature). (A) Both assertion and reason are true; reason correctly explains assertion (B) Both assertion and reason are true; reason does NOT explain assertion (C) Assertion is true; reason is false (D) Assertion is false; reason is true **Answer:** (A) Both assertion and reason are true; reason correctly explains assertion **Reason:** During phase transitions, temperature is constant; latent heat is the energy required to break bonds, not raise kinetic energy. **Q23.** **Assertion:** Dry ice (solid CO₂) placed in a room disappears without leaving any liquid residue. **Reason:** CO₂ undergoes sublimation because the pressure in the room is below the triple point of CO₂. (A) Both assertion and reason are true; reason correctly explains assertion (B) Both assertion and reason are true; reason does NOT explain assertion (C) Assertion is true; reason is false (D) Assertion is false; reason is true **Answer:** (A) Both assertion and reason are true; reason correctly explains assertion **Reason:** At room temperature and atmospheric pressure, CO₂ is below its triple point, so solid sublimes directly to gas without passing through liquid. **Q24.** **Assertion:** Water at the top of a mountain boils faster than water at sea level. **Reason:** The boiling point decreases as atmospheric pressure decreases; therefore, less heat is required to boil water at high altitudes. (A) Both assertion and reason are true; reason correctly explains assertion (B) Both assertion and reason are true; reason does NOT explain assertion (C) Assertion is true; reason is false (D) Assertion is false; reason is true **Answer:** (A) Both assertion and reason are true; reason correctly explains assertion **Reason:** Lower atmospheric pressure reduces the opposing force on vapour formation; water boils at ~70°C on a 2000 m mountain instead of 100°C at sea level. **Q25.** **Assertion:** Evaporation from a lake contributes to global water cycle and freshwater availability in regions far from the lake. **Reason:** Water evaporates, rises as vapour, condenses into clouds, and falls as precipitation in other regions. (A) Both assertion and reason are true; reason correctly explains assertion (B) Both assertion and reason are true; reason does NOT explain assertion (C) Assertion is true; reason is false (D) Assertion is false; reason is true **Answer:** (A) Both assertion and reason are true; reason correctly explains assertion **Reason:** The hydrological cycle ensures water is redistributed globally; evaporation from one region supplies precipitation to another, sustaining freshwater ecosystems. **Q26.** **Assertion:** A sealed container of water at 25°C and 1 atm will NOT boil, even after 24 hours of heating. **Reason:** The pressure inside the sealed container will increase as water evaporates, raising the boiling point above the supply temperature. (A) Both assertion and reason are true; reason correctly explains assertion (B) Both assertion and reason are true; reason does NOT explain assertion (C) Assertion is true; reason is false (D) Assertion is false; reason is true **Answer:** (A) Both assertion and reason are true; reason correctly explains assertion **Reason:** In a sealed container, evaporated vapour increases pressure, which raises the boiling point—a fundamental principle in pressure cookers. **Q27.** **Assertion:** The latent heat of vaporization of water (2260 kJ/kg) is much greater than its latent heat of fusion (334 kJ/kg). **Reason:** Breaking all intermolecular bonds (vaporization) requires more energy than partially breaking them (melting). (A) Both assertion and reason are true; reason correctly explains assertion (B) Both assertion and reason are true; reason does NOT explain assertion (C) Assertion is true; reason is false (D) Assertion is false; reason is true **Answer:** (A) Both assertion and reason are true; reason correctly explains assertion **Reason:** In melting, molecules move from ordered lattice to disordered liquid (some bonds broken). In vaporization, molecules escape entirely, breaking ALL hydrogen bonds. **Q28.** **Assertion:** If 1 kg of ice at 0°C and 1 kg of water at 0°C are exposed to the same heat source for 10 minutes, the water will reach a higher temperature than the melted ice. **Reason:** The ice must first absorb latent heat of fusion before its temperature can rise, whereas liquid water's temperature rises immediately. (A) Both assertion and reason are true; reason correctly explains assertion (B) Both assertion and reason are true; reason does NOT explain assertion (C) Assertion is true; reason is false (D) Assertion is false; reason is true **Answer:** (A) Both assertion and reason are true; reason correctly explains assertion **Reason:** Ice's latent heat (334 kJ/kg) uses up most of the input heat during melting; only remaining heat raises temperature. Liquid water converts all input heat to temperature increase. **Q29.** **Assertion:** Water vapor in the atmosphere is responsible for Earth's greenhouse effect and climate regulation. **Reason:** Water is the most abundant greenhouse gas in the atmosphere, trapping heat and maintaining surface temperature above the freezing point. (A) Both assertion and reason are true; reason correctly explains assertion (B) Both assertion and reason are true; reason does NOT explain assertion (C) Assertion is true; reason is false (D) Assertion is false; reason is true **Answer:** (A) Both assertion and reason are true; reason correctly explains assertion **Reason:** Water vapour accounts for 50% of the natural greenhouse effect; without it, Earth's average temperature would drop ~33°C, making life impossible. **Q30.** **Assertion:** In water-scarce regions, preventing evaporation (e.g., using mulch or covers) is a valid water conservation strategy. **Reason:** Evaporation is an uncontrolled loss of freshwater to the atmosphere, while transpiration from crops is a necessary process that cannot be prevented. (A) Both assertion and reason are true; reason correctly explains assertion (B) Both assertion and reason are true; reason does NOT explain assertion (C) Assertion is true; reason is false (D) Assertion is false; reason is true **Answer:** (A) Both assertion and reason are true; reason correctly explains assertion **Reason:** NCERT emphasizes water conservation in arid regions by reducing evaporative losses from soil while maintaining essential plant transpiration for food production.

CBSE examiners deliberately design wrong options to catch common misconceptions. Here are the most frequent traps in Chapter 8: **Trap 1: Confusing Boiling with Evaporation.** A question might ask "At what temperature does water change to gas?" Students who don't read carefully choose "100°C" (boiling point) when the correct answer is "any temperature above 0°C" (evaporation). Boiling is rapid, occurs throughout the liquid at a fixed temperature. Evaporation is slow, occurs at the surface at any temperature. Read the context: is it asking about a specific phase change or a general process? **Trap 2: Assuming Ice and Snow Are Different.** Snow is frozen water vapor (solid form). Ice is frozen liquid water. Both are solid H₂O, but the MCQ may ask which is the solid state, and students may overthink by choosing "snow" when "ice" is the chapter-specific example. **Trap 3: Mixing Up Latent Heat Values.** Students often reverse the latent heat of fusion (334 kJ/kg) and vaporization (2260 kJ/kg). Trap options use both values; the larger value (vaporization) is the correct answer for gas formation. Memorize: vaporization > fusion. **Trap 4: Misunderstanding Sublimation.** A question like "Which process is the opposite of sublimation?" has no direct opposite in the traditional list. Deposition (gas → solid) is the opposite, but it's rarely the correct answer in trap questions. Students fall for "melting" or "evaporation" if they don't read carefully. **Trap 5: Confusing Condensation with Freezing.** Both are processes that form solid or liquid from a gas/liquid, but they're different. Condensation: gas → liquid. Freezing: liquid → solid. A question on dew formation should be answered as "condensation," not "freezing." **Trap 6: Pressure and Boiling Point Reversal.** Students sometimes think "higher pressure means lower boiling point" (opposite of reality). High altitude (low pressure) → low boiling point. Pressure cooker (high pressure) → high boiling point. If the option says the reverse, it's a trap. **Trap 7: Water Cycle Oversimplification.** A question may ask "Where does all evaporated water go?" A trap option says "returns as rain immediately." The correct answer accounts for transpiration, infiltration, and groundwater storage—it's a cycle, not a one-step process. **Trap 8: Assertion-Reason Pitfalls.** Even if both assertion and reason are true, they must be logically connected. A trap option states both as true but separates them logically. Example: "Ice melts at 0°C (true) because water is transparent (true, but irrelevant)." The answer is (B), not (A). **Pro Tip:** When in doubt, refer back to NCERT definitions. CBSE examiners reward students who use textbook language. If Chapter 8 defines melting as "the process by which a solid changes to liquid," use exactly that phrasing in your reasoning.

The CBSE Class 9 Science exam is 90 minutes for 60 marks, with approximately 20–25 MCQs per paper. Effective time management is the difference between scoring 55% and 85%. **Step 1: Pre-Exam Sorting (First 2 Minutes).** Scan all MCQs and mentally sort them: Easy (straight definition recall), Medium (concept application), and Hard (assertion-reason). Don't attempt in order; this wastes time on hard questions you might miss. **Step 2: Solve Easy MCQs First (5–7 Minutes for 5–8 Questions).** These require 30–45 seconds each. Examples: "What is the melting point of ice?" or "Which process is opposite to melting?" Secure these marks first; they build confidence and provide a buffer for harder questions. **Step 3: Attempt Medium MCQs (15–20 Minutes for 8–10 Questions).** These require 90–120 seconds each. You'll need to think through water cycle dynamics, pressure-boiling relationships, or latent heat calculations. If you're stuck after 90 seconds, skip and return later. **Step 4: Tackle Hard Assertion-Reason MCQs (20–25 Minutes for 5–7 Questions).** These are worth the same points as easy MCQs, so don't lose track of time. Spend max 3 minutes per assertion-reason question. Read the assertion, then the reason, then evaluate the logic. If unsure, check option (B) first: "Both true but not logically connected" is a common answer. **Step 5: Review & Bubble Corrections (Last 5 Minutes).** Don't mark answers directly in the question paper. Use a rough sheet for work, then mark the OMR sheet carefully. In the final 5 minutes, double-check your most doubtful answers. Change an answer ONLY if you're 90% sure; blind guessing introduces errors. **Chapter 8 Specific Timing Tips:** - Water cycle questions ("Where does evaporated water go?") take 2 minutes; visualize the cycle as you read. - Pressure-boiling questions (mountain vs. sea level) require you to reason through the inverse relationship; allocate extra time. - Latent heat calculations rarely appear in CBSE Class 9 MCQs, but if they do, set up the formula (Q = m × L) and substitute immediately. - Assertion-reason on phase transitions (melting vs. freezing) often have trap options; read twice. **Mental Tricks:** 1. **Elimination:** If you can rule out 2 options in 20 seconds, you've halved the guessing risk. 2. **Keywords:** Look for words like "always," "never," "only." These often indicate trap options. Example: "Boiling ONLY occurs at 100°C" is false; it depends on pressure. 3. **Anchor Facts:** Memorize the 5 constants from NCERT: melting point (0°C), boiling point (100°C), latent heat of fusion (334 kJ/kg), latent heat of vaporization (2260 kJ/kg), and density of water (1000 kg/m³). These appear in ~40% of Chapter 8 MCQs. **After the Exam:** Review each MCQ you guessed or left blank. Did you misunderstand the concept or misread the question? Log these patterns; they reveal your weak areas. Practice 10 similar MCQs daily for 3 days, and your score will jump 5–10% in the next mock exam. Start a 3-day free trial at cbsetutor.ai to access adaptive MCQ drills with instant feedback and personalized weak-point analysis.

Before your exam, verify you can answer these six core questions without referring to your notes: **1. Three States of Matter:** Can you define and give examples of solid, liquid, and gas in 1 minute? (Solid: fixed shape & volume, e.g., ice. Liquid: fixed volume, takes container shape, e.g., water. Gas: no fixed shape or volume, e.g., steam.) **2. Phase Transitions:** Do you know all six transitions? Melting (solid → liquid), freezing (liquid → solid), evaporation (liquid → gas), condensation (gas → liquid), sublimation (solid → gas), deposition (gas → solid). Can you name a real-world example for each? **3. Melting vs. Boiling:** Why is melting at 0°C but boiling at 100°C? (Melting: minimum energy to break lattice order; boiling: molecules need energy to overcome all intermolecular forces AND escape the liquid surface.) Why does boiling point depend on pressure? (Lower pressure = lower boiling point; molecules need less kinetic energy.) **4. Evaporation & Condensation:** Which is endothermic and which is exothermic? (Evaporation absorbs heat; condensation releases heat.) Can you explain why wet hair feels cool when air-drying? (Evaporating water on hair absorbs heat, cooling the scalp.) **5. Water Cycle:** Can you draw and label the cycle? (Evaporation from oceans/lakes → Condensation in atmosphere (clouds) → Precipitation (rain/snow) → Infiltration into soil → Groundwater / Surface runoff back to oceans. Include transpiration from plants.) **6. Water Conservation:** Why is freshwater scarce if water cycle is continuous? (97% of Earth's water is saltwater; 3% is freshwater, 2% is locked in ice caps/glaciers, leaving <1% accessible for humans. Human activities and climate change are reducing this further.) If you hesitate on any of these, spend 20 minutes reviewing that section in NCERT Chapter 8 before the exam.