1. Which state of matter has a definite shape and definite volume?
(A) Solid
(B) Liquid
(C) Gas
(D) Plasma
Answer: (A) Solid
Explanation: Solids have closely packed particles and therefore retain both their shape and volume.
2. Which state of matter has a definite volume but no definite shape?
(A) Solid
(B) Liquid
(C) Gas
(D) Plasma
Answer: (B) Liquid
Explanation: A liquid takes the shape of its container but retains a definite volume.
3. Which state of matter has neither a definite shape nor a definite volume?
(A) Solid
(B) Liquid
(C) Gas
(D) Ice
Answer: (C) Gas
Explanation: Gas particles are widely separated and move freely, so gases occupy the entire available container.
4. Which of the following is a physical change?
(A) Burning of wood
(B) Rusting of iron
(C) Melting of ice
(D) Curdling of milk
Answer: (C) Melting of ice
Explanation: Melting changes the physical state of water without producing a new substance.
5. Which of the following is a chemical change?
(A) Melting of wax
(B) Boiling of water
(C) Dissolving sugar in water
(D) Rusting of iron
Answer: (D) Rusting of iron
Explanation: Rusting produces a new substance, iron oxide, so it is a chemical change.
6. Which of the following is an example of a physical change?
(A) Burning paper
(B) Formation of curd
(C) Cutting paper
(D) Digestion of food
Answer: (C) Cutting paper
Explanation: Cutting changes only the size and shape of the paper, not its chemical composition.
7. Which of the following is an example of a chemical change?
(A) Freezing water
(B) Evaporation of water
(C) Breaking glass
(D) Burning of coal
Answer: (D) Burning of coal
Explanation: Burning produces new substances such as carbon dioxide and ash.
8. The density of a substance is defined as:
(A) Volume per unit mass
(B) Mass per unit volume
(C) Mass × volume
(D) Weight per unit area
Answer: (B) Mass per unit volume
Explanation: Density is the ratio of mass to volume.
9. A substance has a mass of 200 g and a volume of 50 cm³. Its density is:
(A) 2 g/cm³
(B) 4 g/cm³
(C) 10 g/cm³
(D) 250 g/cm³
Answer: (B) 4 g/cm³
Explanation: Density = mass ÷ volume = 200 ÷ 50 = 4 g/cm³.
10. An object floats on water when its average density is:
(A) Greater than water
(B) Less than water
(C) Equal to zero
(D) Always greater than air
Answer: (B) Less than water
Explanation: An object with average density less than the liquid can float.
11. The spreading of perfume smell throughout a room is an example of:
(A) Evaporation
(B) Diffusion
(C) Sublimation
(D) Condensation
Answer: (B) Diffusion
Explanation: Perfume molecules move from a region of higher concentration to regions of lower concentration.
12. Diffusion occurs fastest in:
(A) Solids
(B) Liquids
(C) Gases
(D) All at the same rate
Answer: (C) Gases
Explanation: Gas particles have large spaces between them and move rapidly.
13. The smell of cooking food reaches another room mainly because of:
(A) Condensation
(B) Diffusion
(C) Freezing
(D) Sublimation
Answer: (B) Diffusion
14. Evaporation is the process in which:
(A) A liquid changes into a gas from its surface
(B) A gas changes into a liquid
(C) A solid changes directly into a gas
(D) A liquid changes into a solid
Answer: (A) A liquid changes into a gas from its surface
15. Which factor generally increases the rate of evaporation?
(A) Decrease in temperature
(B) Increase in humidity
(C) Increase in surface area
(D) Decrease in wind speed
Answer: (C) Increase in surface area
Explanation: Greater surface area allows more liquid molecules to escape from the surface.
16. Wet clothes dry faster on a windy day because:
(A) Wind decreases the surface area
(B) Moving air removes water vapour from around the clothes
(C) Wind increases the boiling point of water
(D) Wind freezes the water
Answer: (B) Moving air removes water vapour from around the clothes
17. Sweating cools the human body mainly because:
(A) Sweat freezes on the skin
(B) Evaporation of sweat removes heat from the body
(C) Sweat increases body temperature
(D) Sweat prevents heat loss
Answer: (B) Evaporation of sweat removes heat from the body
18. Which substance undergoes sublimation?
(A) Common salt
(B) Camphor
(C) Sand
(D) Iron
Answer: (B) Camphor
Explanation: Camphor can change directly from solid to vapour without passing through the liquid state under suitable conditions.
19. Which of the following is an example of sublimation?
(A) Ice → water
(B) Water → steam
(C) Camphor → vapour
(D) Steam → water
Answer: (C) Camphor → vapour
20. Which of the following correctly represents a physical change → chemical change pair?
(A) Melting ice → rusting iron
(B) Burning wood → boiling water
(C) Curdling milk → freezing water
(D) Digestion → melting wax
Answer: (A) Melting ice → rusting iron
Explanation: Melting ice is a physical change, whereas rusting iron produces a new substance and is a chemical change.
Quick Revision
| Concept | Must Remember |
|---|---|
| Solid | Definite shape + volume |
| Liquid | Definite volume, no definite shape |
| Gas | No definite shape or volume |
| Physical change | No new substance formed |
| Chemical change | New substance formed |
| Density | Mass per unit volume |
| Diffusion | Movement from high to low concentration |
| Evaporation | Liquid → gas from surface |
| Sublimation | Solid → gas directly |
| Perfume smell | Diffusion |
| Wet clothes drying | Evaporation |
| Sweating | Evaporation |
| Camphor | Sublimation |
| Rusting | Chemical change |
| Melting ice | Physical change |