CBSE Class 9 Chemistry Matter in Our Surroundings MCQs Set 09

Answer: (c) Mass

Explanation:
1. Mass is the quantity of matter in an object.
2. Weight is the force of gravity on it, gram is a unit and density is mass per unit volume.

Teacher's Note:
1. Mass does not change from place to place.
2. Weight changes with gravity.

Answer: (a) Feeling hot

Explanation:
1. Matter has mass and occupies space.
2. Smoke, humidity (water vapour) and water are matter.
3. Feeling hot is a sensation, not matter.

Teacher's Note:
1. Feelings, thoughts, light and heat are not matter.
2. Check mass and volume.

Answer: (c) Hydrogen

Explanation:
1. Lighter gases diffuse faster.
2. Hydrogen has the smallest molar mass, so it diffuses fastest.

Teacher's Note:
1. Rate of diffusion decreases as molar mass increases.
2. Graham's law of diffusion.

Answer: (d) Gas > Liquid > Solid

Explanation:
1. Particles of gases move freely and randomly, those of liquids move less freely and those of solids only vibrate about fixed positions.
2. So the order is gas > liquid > solid.

Teacher's Note:
1. More free movement means more randomness.
2. Solids are the most ordered.

Answer: (d) diffusion

Explanation:
1. Particles of potassium permanganate spread through the water on their own.
2. This mixing of particles is diffusion.

Teacher's Note:
1. Diffusion happens in solids, liquids and gases.
2. It is fastest in gases.

Answer: (a) liquid only

Explanation:
1. Sugar dissolves completely in water, forming a uniform solution.
2. Only one phase, liquid, remains.

Teacher's Note:
1. A solution is a homogeneous mixture.
2. If sugar remained undissolved, there would be two phases.

Answer: (a) Both P and Q are true and Q explains P

Explanation:
1. Oxygen diffuses from air into water and dissolves, so it is available to aquatic animals.
2. Both statements are true and the second explains the first.

Teacher's Note:
1. Dissolved oxygen supports aquatic life.
2. Warm water holds less dissolved oxygen.

Answer: (a) sodium chloride

Explanation:
1. Sodium chloride is an ionic solid with strong electrostatic forces between ions.
2. Hydrogen and carbon dioxide are gases and ether is a volatile liquid.

Teacher's Note:
1. Ionic solids have very strong forces.
2. That is why NaCl melts only at about 800 degrees C.

Answer: (a) Matter is continuous in nature

Explanation:
1. Matter is made of tiny particles with spaces between them, so it is not continuous.
2. The other statements are correct.

Teacher's Note:
1. Particle nature of matter is a basic idea.
2. Diffusion and dissolving show spaces between particles.

Answer: (c) Solids have only one free surface

Explanation:
1. A solid has a fixed shape bounded by several surfaces, not just one free surface.
2. A liquid has one free surface.
3. The other statements about solids and gases are correct.

Teacher's Note:
1. Liquids in a container show a single free upper surface.
2. Solids have a definite shape.

Answer: (a) Solids

Explanation:
1. Particles are packed most closely in solids, so solids are generally the densest state of matter.

Teacher's Note:
1. Gas particles are far apart and plasma is a very thin ionised gas.
2. Water is an exception where ice is less dense.

Answer: (d) all of these

Explanation:
1. Different liquids have different densities, viscosities and solubilities.
2. So all three are different.

Teacher's Note:
1. Properties of matter depend on particle forces.
2. Honey is far more viscous than water.

Answer: (b) Bromine

Explanation:
1. Bromine is a liquid at room temperature, whereas hydrogen chloride, fluorine and chlorine are gases.
2. So bromine has the strongest forces of attraction.

Teacher's Note:
1. A liquid has stronger forces than a gas.
2. Heavier halogens have stronger forces.

Answer: (c) gases consist of molecules having very large intermolecular space which can be reduced or increased under ordinary conditions

Explanation:
1. Gas molecules are far apart, so a gas can be squeezed into a smaller volume.
2. The large space also lets the molecules spread out to fill any container.

Teacher's Note:
1. Gases are compressible because of the large empty space.
2. Solids and liquids are hardly compressible.

Answer: (a) increases with increase in temperature

Explanation:
1. When a gas is heated, its particles move faster and push outward.
2. At constant pressure the volume increases (Charles's law).

Teacher's Note:
1. Volume is directly proportional to Kelvin temperature at constant pressure.
2. Cooling reduces volume.

Answer: (b) its boiling point becomes more than 100 degrees C

Explanation:
1. A dissolved non-volatile solute raises the boiling point of the solvent.
2. So the solution boils above 100 degrees C.

Teacher's Note:
1. Impurities raise the boiling point and lower the freezing point.
2. This is used in making antifreeze.

Answer: (a) interparticle forces of attraction decrease

Explanation:
1. During melting the particles gain energy and the forces holding them in fixed places become weaker.
2. The temperature stays constant during melting, and the compressibility remains very small.

Teacher's Note:
1. Heat supplied during melting does not raise the temperature.
2. It is used to overcome forces between particles.

Answer: (a) absorbed

Explanation:
1. Melting needs energy to break the ordered arrangement in ice.
2. Heat is therefore absorbed (latent heat of fusion).

Teacher's Note:
1. Melting is endothermic.
2. Freezing releases the same heat.

Answer: (b) Crushing a crystal

Explanation:
1. Crushing a crystal only breaks it into smaller pieces and does not change its state.
2. Temperature, pressure and heat can change the state.

Teacher's Note:
1. A state change needs a change in particle energy or forces.
2. Crushing is a physical change of size only.

Answer: (b) 40 degrees C

Explanation:
1. The melting point and freezing point of a pure substance are the same temperature.
2. So the freezing point is 40 degrees C.

Teacher's Note:
1. The same temperature is observed whether we heat or cool.
2. Mixtures do not behave this way.