Changes around us

Which of the following describes a chemical property of a substance?

• A. Colourless

• B. Odourless

• C. A liquid at 20°C

• Reacts with oxygen

Which of the following is a chemical reaction?

• A. Hydrogen and oxygen combine to form water

• B. Liquid water freezes and becomes ice

• C. A rock is crushed into small pieces

• D. Sugar dissolves in hot tea

Rohit heated water until it became a gas. Which of the following terms describes this change?

• A. Boiling

• B. Freezing

• C. Condensing

• D. Melting

A pan of water boils until it all evaporates into the air. Which of the following properties of the water remains the same after this change?

• A. Its mass

• B. Its temperature

• C. Its state

• D. Its volume

While lighting a candle, Paheli observed the following changes (i) Wax was melting. (ii) Candle was burning. (iii) Size of the candle was reducing. (iv) Melted wax was getting solidified. Of the above, the changes that can be reversed are

• (a) (i) and (ii)

• (b) (ii) and (iii)

• (c) (iii) and (iv)

• (d) (i) and (iv)

An ice cube melts into the water and the change is considered as reversible change. Which factor would reverse the change?

• (a)Increase in weight of the water

• (b)Decrease in weight of the water

• (c)Increase in temperature of water

• (d)Decrease in temperature of water

Which factor is responsible for the expansion and contraction of a metallic rod?

• (a)Change in shape temperature of rod

• (b)Change in weight

• (c)Change in type of material

• (d)Change in temperature of rod

A student cuts a square piece of paper into 4 small square pieces as shown. What makes this change an irreversible change?

• (a)Addition of heat

• (b)Change in shape

• (c)Reduction of size

• (d)Difference in colour

When a bud changes into a flower it undergoes:

• A. A chemical change

• B. An irreversible change

• C. A permanent change

• D. All of the above

Iron rim is made slightly smaller than the wooden wheel. The rim is usually heated before fixing into the wooden wheel, because on heating the iron rim

• (a) expands and fits onto the wooden wheel.

• (b) contracts and fits onto the wooden wheel.

• (c) no change in the size takes place.

• (d) expands first, then on cooling contracts and fits onto the wooden wheel.