Class 9 – Science Extra Questions – Ch. 1 – Matter in Our Surroundings

Ans: B

Explanation: The earthen pot has small pores. Water seeps through these pores and evaporates from the outer surface of the pot. The process of evaporation requires heat energy. This heat energy is absorbed from the surrounding water inside the pot, causing the water inside to cool down.
Correct Option: B

Ans: B

Explanation: When a substance is undergoing a phase change, such as melting, its temperature remains constant as the heat energy supplied is used to break the intermolecular bonds and convert the solid into a liquid. Once all the ice has melted into liquid water, the temperature of the water will then begin to increase as it absorbs more heat. Therefore, the ice’s temperature does not increase at all while it is melting.
Correct Option: B

Ans: A

Explanation: Iodine tincture, a common antiseptic, is a solution of iodine dissolved in alcohol. The alcohol acts as a solvent and also contributes to the antiseptic properties. While iodine can be dissolved in other substances, the specific formulation known as “iodine tincture” uses alcohol.
Correct Option: A

Ans: C

Explanation: When a jar of air is placed over a jar of bromine vapor, the bromine vapor will be observed to slowly move downwards and mix with the air. This demonstrates that bromine vapor is denser than air, causing it to settle. Option D is incorrect because bromine is a gas and its movement is driven by diffusion and density differences, not solely by gravity in a way that would prevent downward movement if it were denser.
Correct Option: C

Ans: C

Explanation: The question asks for the process where a solid changes directly into a gas, bypassing the liquid state. Let’s examine the options:
A. Vaporisation is the general term for a liquid turning into a gas (evaporation and boiling).
B. Fusion is the process of a solid melting into a liquid.
C. Sublimation is the specific term for a solid transitioning directly into a gas.
D. Freezing is the process of a liquid turning into a solid.
Therefore, sublimation is the correct term for a solid turning directly into a gas.
Correct Option: C

Ans: B

Explanation: The transition of water from a liquid to a gas at standard atmospheric pressure is known as vaporization. Freezing is the transition from liquid to solid, condensation is the transition from gas to liquid, and melting is the transition from solid to liquid.
Correct Option: B

Ans: C

Explanation: The boiling point of water is the temperature at which water turns into steam at a given pressure. At standard atmospheric pressure (1 atmosphere), this temperature is 100 degrees Celsius. 0°C is the freezing point of water. 25°C is a common room temperature. 373°C is the boiling point of water in Kelvin.
Correct Option: C

Ans: D

Explanation:The freezing point of substance X is -33°C, meaning it exists as a solid below this temperature and as a liquid above this temperature. The boiling point of substance X is 66°C, meaning it exists as a liquid below this temperature and as a gas above this temperature.
Option A states that at -100°C, X exists in solid state. Since -100°C is well below the freezing point of -33°C, X will be in the solid state.
Option B states that at 0°C, X exists in liquid state. Since 0°C is above the freezing point (-33°C) and below the boiling point (66°C), X will be in the liquid state.
Option C states that at 90°C, X exists in gaseous state. Since 90°C is above the boiling point of 66°C, X will be in the gaseous state.
Therefore, all the statements A, B, and C are correct.
Correct Option: D

Ans: A

Explanation: Temperature is a measure of the average kinetic energy of the particles in a substance. As temperature increases, the particles gain more kinetic energy, move faster, and collide more frequently and with greater force. This increased molecular motion leads to a faster rate of evaporation (liquid turns to gas), diffusion (movement of particles from high to low concentration), and expansion of gases (gases occupy more volume at higher temperatures due to increased molecular motion and collisions with the container walls). Solubility of solids in liquids generally increases with temperature, but the solubility of gases in liquids typically decreases with temperature. Compression of gases is a process that reduces volume, not directly sped up by temperature increase; rather, it’s about external pressure. Therefore, evaporation, diffusion, and expansion of gases are all processes that are directly sped up by an increase in temperature.
Correct Option: A

Ans: A

Explanation: The specific latent heat of vaporization of water is the amount of energy required to change 1 kilogram of water from liquid to gas at its boiling point without a change in temperature. This value is a well-established physical constant for water. The accepted value at standard atmospheric pressure (100°C) is approximately 2.25 × 10^6 J/kg. Option A matches this value.
Correct Option: A