CBSE Class 9 Science Advanced Chemistry Matter in Our Surrounding MCQs Set 01

Answer: (c) mass

Explanation:
1. Mass is the amount of matter in a body.
2. Weight is the pull of gravity, volume is the space occupied and density is mass per unit volume.
3. So the answer is mass.

Teacher's Note:
1. Learn the pair: mass means amount of matter, volume means space taken.
2. Mass stays the same everywhere, but weight can change from place to place.

Answer: (a) Solids

Explanation:
1. Rigid means unbending, able to keep its shape under a force.
2. Only solids keep their shape; liquids and gases flow and are called fluids.
3. The answer is solids.

Teacher's Note:
1. Liquids and gases together are called fluids.
2. A solid keeps its own shape because its particles are held tightly.

Answer: (d) All of the above

Explanation:
1. In solids the particles are packed closest, so the force between them is greatest and the spaces are smallest.
2. In gases the particles are far apart, so the force is smallest.
3. Statements (A), (B) and (C) are all true, so the answer is all of the above.

Teacher's Note:
1. Remember the order of force: solid > liquid > gas.
2. The order of spaces between particles is the opposite.

Answer: (d) No change in volume.

Explanation:
1. Sugar particles fit into the gaps between water particles.
2. So the total volume of the solution stays the same.
3. The answer is no change in volume.

Teacher's Note:
1. This simple experiment shows that there are spaces between particles of matter.
2. It works only for a small amount of sugar; too much would not all dissolve.

Answer: (d) Both (B) and (C)

Explanation:
1. A gas has a definite mass.
2. A gas has neither a definite shape nor a definite volume, because it fills its container.
3. So (B) and (C) are wrong statements and the answer is both (B) and (C).

Teacher's Note:
1. Read the word 'not' in the question carefully.
2. A gas takes the shape and volume of its container.

Answer: (b) Feeling of cold

Explanation:
1. Air and dust occupy space and have mass, so they are matter.
2. A feeling of cold is only a sensation; it has no mass and takes no space.
3. The answer is feeling of cold.

Teacher's Note:
1. Matter means anything with mass that takes up space.
2. Feelings, heat and light are not matter either.

Answer: (d) All are correct

Explanation:
1. Gas particles are far apart, so the spaces are largest (A is true).
2. They collide again and again and keep changing direction, so their path is zig-zag (B is true).
3. Solids are packed closest (C is true).
4. The answer is all are correct.

Teacher's Note:
1. Gas particles move randomly and collide with each other and the walls.
2. Compact means tightly packed.

Answer: (b) Liquids can be compressed easily, but not gases.

Explanation:
1. Statements (A), (C) and (D) agree with what we know.
2. Gases are compressed far more easily than liquids, so the reverse statement in (B) is wrong.
3. The answer is (B).

Teacher's Note:
1. Gases have the largest spaces, so they are the easiest to compress.
2. Liquids are only slightly compressible.

Answer: (d) All of these

Explanation:
1. Large amounts of gas can be squeezed into a small cylinder because gases are highly compressible.
2. This is used for LPG, oxygen cylinders and CNG.
3. The answer is all of these.

Teacher's Note:
1. LPG is liquefied petroleum gas and CNG is compressed natural gas.
2. In all cases a big volume of gas is stored in a small cylinder.

Answer: (b) Fluidity is the maximum in the liquid state.

Explanation:
1. Liquids flow, so they are fluids, but gases flow even more easily.
2. Fluidity is maximum in the gaseous state, so (B) does not go with liquids.
3. The answer is (B).

Teacher's Note:
1. Fluidity order: gas > liquid > solid.
2. The other three statements are true for liquids.

Answer: (c) (A) & (B) both

Explanation:
1. Heating or cooling (temperature) changes the state of matter.
2. Raising or lowering the pressure can also change it, for example liquefying a gas.
3. The answer is (A) and (B) both.

Teacher's Note:
1. Temperature and pressure together decide the state of a substance.
2. High pressure and low temperature liquefy gases.

Answer: (a) are same.

Explanation:
1. Ice melts at 0 °C, and water freezes at the same 0 °C.
2. So the two are the same, option (A).

Teacher's Note:
1. Melting point of a solid and freezing point of its liquid are numerically equal.
2. The same is true for boiling and condensation points.

Answer: (b) 351 K

Explanation:
1. Kelvin = Celsius + 273.
2. T = 78 + 273 = 351 K.

Teacher's Note:
1. Add 273 to a Celsius reading to get Kelvin.
2. 373 K is the boiling point of water, so (A) is a trap.

Answer: (b) 22.5 × 10⁵ J/kg

Explanation:
1. The latent heat of vaporisation of water is about 22.5 × 10⁵ J/kg, that is roughly 2.26 × 10⁶ J/kg.
2. 3.34 × 10⁵ J/kg is the latent heat of fusion of ice, so (C) is wrong.
3. The answer is (B).

Teacher's Note:
1. Vaporisation needs much more heat than fusion: about 22.5 × 10⁵ against 3.34 × 10⁵ J/kg.
2. The book gives 22.5 × 10⁵ in one place and 22.6 × 10⁵ in another; the accurate value is 22.6 × 10⁵ J/kg.

Answer: (a) Kelvin

Explanation:
1. The SI unit of temperature is the kelvin (K).
2. Celsius is a common unit but not the SI unit.
3. The answer is Kelvin.

Teacher's Note:
1. Remember: K for SI, °C for everyday use.
2. Note that we write K, not °K.

Answer: (c) solid changes directly into gas.

Explanation:
1. Sublimation skips the liquid stage.
2. A solid turns directly into vapour on heating, so the answer is (C).

Teacher's Note:
1. Camphor, naphthalene and ammonium chloride sublime.
2. The reverse change, vapour directly to solid, is also called sublimation in this book.

Answer: (d) is absorbed as latent heat of vaporisation by the liquid.

Explanation:
1. During boiling the temperature stays constant, so (B) and (C) are wrong.
2. The heat is used to break the forces between the particles and change the liquid to gas.
3. This hidden heat is the latent heat of vaporisation, option (D).

Teacher's Note:
1. Constant temperature during a change of state means the heat is going into the change itself.
2. That is why it is called latent (hidden) heat.

Answer: (b) Crushing a crystal

Explanation:
1. Heat (temperature), pressure and even electricity (as in a discharge tube, forming plasma) can change the state.
2. Crushing a crystal only breaks it into smaller pieces of the same solid.
3. The answer is crushing a crystal.

Teacher's Note:
1. The state changes only when the arrangement and energy of particles change.
2. Crushing changes size, not state.

Answer: (c) Camphor

Explanation:
1. Camphor changes directly from solid to vapour on heating.
2. Common salt, sugar and potassium nitrate melt or decompose instead.
3. The answer is camphor.

Teacher's Note:
1. Other examples are naphthalene, iodine and ammonium chloride.
2. Sublimation is used to separate such solids from other materials.

Answer: (a) Gases are highly compressible and diffuse very easily.

Explanation:
1. Gases have large spaces and weak forces, so they compress and diffuse easily (A is true).
2. Gases do not have strong forces, so (B) is false.
3. Solids are packed closely but are almost incompressible, so (C) is false.
4. Solids are not loosely packed, so (D) is false.

Teacher's Note:
1. Check each statement separately for the two properties it mentions.
2. Tight packing goes with strong forces and negligible compressibility.

Answer: (a) the temperature of the liquid falls.

Explanation:
1. The fastest particles leave the surface and take their energy with them.
2. The remaining liquid has less average energy, so it cools.
3. The answer is (A).

Teacher's Note:
1. This is called cooling by evaporation.
2. It is why a wet cloth feels cold.

Answer: (a) increases.

Explanation:
1. More particles gain enough kinetic energy to escape at a higher temperature.
2. So the rate of evaporation increases.

Teacher's Note:
1. Clothes dry faster on a hot day.
2. Rate of evaporation is directly related to temperature.

Answer: (b) is less.

Explanation:
1. Humid air already holds a lot of water vapour.
2. It can take up only a little more, so evaporation is slow.
3. The answer is (B) is less.

Teacher's Note:
1. Humidity and rate of evaporation vary in opposite ways.
2. This is why clothes dry slowly in the rainy season.

Answer: (a) from the surface.

Explanation:
1. Evaporation is a surface phenomenon.
2. Only particles at the surface can escape into the air.
3. The answer is from the surface.

Teacher's Note:
1. Boiling, on the other hand, is a bulk phenomenon.
2. That is why a larger surface area speeds up evaporation.

Answer: (d) All of these

Explanation:
1. Higher temperature, larger surface area and lower humidity all increase evaporation.
2. Wind speed also matters.
3. The answer is all of these.

Teacher's Note:
1. Four main factors: temperature, surface area, humidity and wind speed.
2. The nature of the liquid also counts.

Answer: (a) Evaporation

Explanation:
1. Evaporation can happen at any temperature below the boiling point.
2. Boiling needs exactly the boiling point, and condensation is the reverse change.
3. The answer is evaporation.

Teacher's Note:
1. Wet clothes dry at room temperature by evaporation.
2. Water boils only at 100 °C at normal pressure.

Answer: (d) Evaporation

Explanation:
1. The earthen pot has tiny pores through which water seeps out.
2. This water evaporates and takes latent heat from the water inside, cooling it.
3. The answer is evaporation.

Teacher's Note:
1. Cooling by evaporation also works in a desert cooler.
2. Transpiration is a process in plants, so it does not apply here.

Answer: (a) Evaporation leads cooling

Explanation:
1. Dogs have few sweat glands.
2. Saliva evaporating from the tongue takes heat away and cools the body.
3. The answer is (A).

Teacher's Note:
1. Panting is the dog's way of getting cooling by evaporation.
2. Condensation would warm, not cool, the tongue.

Answer: (b) Is more in non coastal areas than in coastal areas

Explanation:
1. Coastal air is humid because of the sea.
2. High humidity slows evaporation, so evaporation is faster in drier non coastal areas.
3. The answer is (B).

Teacher's Note:
1. Link the answer to humidity.
2. Drier air takes up more water vapour.

Answer: (a) Depth of liquid

Explanation:
1. Humidity, temperature and surface area (surface of liquid) all change the rate.
2. Evaporation happens at the surface, so the depth of the liquid does not matter.
3. The answer is depth of liquid.

Teacher's Note:
1. Surface area matters, depth does not.
2. A deep and a shallow pan with the same top area dry at the same rate.

Answer: (a) iron bar

Explanation:
1. Iron is a solid, water is a liquid, and air and nitrogen are gases.
2. Forces are strongest in solids.
3. The answer is iron bar.

Teacher's Note:
1. Pick the solid in such questions.
2. Gases have the weakest forces.

Answer: (a) Adhesive force between water and glass

Explanation:
1. Force between particles of different substances is adhesive force.
2. Water and glass are different substances, so the force is adhesive.
3. The answer is (A).

Teacher's Note:
1. Cohesion means like particles, adhesion means unlike particles.
2. Cohesive force cannot be 'between water and glass'.

Answer: (c) Solids have only one free surface

Explanation:
1. Solid particles only vibrate about fixed positions (A is true).
2. Solids are almost incompressible (B is true).
3. A solid has many surfaces, not only one, so (C) is wrong.
4. Gases diffuse very fast (D is true).
5. The answer is (C).

Teacher's Note:
1. A liquid has one free surface, but a solid has many.
2. Find the false statement by testing each one.

Answer: (c) Viscosity

Explanation:
1. Viscosity is the resistance of a liquid to flow.
2. This friction between layers stops the motion after some time.
3. The answer is viscosity.

Teacher's Note:
1. Honey is more viscous than water.
2. Fluidity is the opposite of viscosity.

Answer: (a) its melting point decreases.

Explanation:
1. Salt mixed with ice lowers the melting point to below 0 °C.
2. That is why salt is spread on icy roads.
3. The answer is (A).

Teacher's Note:
1. Impurities lower the melting point of ice.
2. Ice with salt gets colder than 0 °C and is used in ice-cream making.

Answer: (b) Evaporation of liquid takes place only at its boiling point.

Explanation:
1. Statements (A), (C) and (D) are true.
2. Evaporation happens at any temperature below the boiling point, so (B) is false.
3. The answer is (B).

Teacher's Note:
1. It is boiling, not evaporation, which occurs at the boiling point only.
2. Read the word 'false' carefully.

Answer: (a) Saturated vapour pressure of water becomes equal to the atmospheric pressure

Explanation:
1. A liquid boils when its vapour pressure rises to equal the pressure of the atmosphere.
2. Then bubbles of vapour can form inside the liquid.
3. The answer is (A).

Teacher's Note:
1. At higher altitude the air pressure is lower, so boiling starts at a lower temperature.
2. Pressure cookers raise the pressure and so the boiling point.

Answer: (a) latent heat of fusion.

Explanation:
1. During melting the heat supplied is used to change the state, not to raise the temperature.
2. This heat is the latent heat of fusion.
3. The answer is (A).

Teacher's Note:
1. Melting means fusion.
2. Vaporisation goes with boiling and sublimation with solid to gas.

Answer: (c) solid into liquid.

Explanation:
1. Fusion is another name for melting.
2. A solid changes into a liquid, so the answer is (C).

Teacher's Note:
1. Freezing is the reverse of fusion.
2. Liquid into gas is vaporisation.

Answer: (b) heat was used for changing ice at 0ºC to water at 0ºC

Explanation:
1. While the ice melts, the heat goes into changing ice at 0 °C to water at 0 °C.
2. So the thermometer reading stays at 0 °C.
3. The answer is (B).

Teacher's Note:
1. The heat used is the latent heat of fusion.
2. Densities have nothing to do with the temperature staying constant.