Physical and Chemical Changes

Pick the change that can be reversed from the following

• Cutting of trees

• Melting of ghee

• Burning of candle

• Blooming of flower

Which of the following change cannot be reversed?

• Melting of chocolate

• Opening a door

• Freezing of ice cream

• Hardening of cement

An iron ring is heated. Which of the following statement about it is incorrect?

• The ring expands.

• The ring almost comes to the same size on cooling.

• The change in this case is reversed.

• The ring changes its shape and the change cannot be reversed.

While lighting a candle, Athena 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

• (i) and (iv)

• (iii) and (iv)

• (ii) and (iii)

• (i) and (ii)

Salt can be separated from its solution (salt dissolved in water), because

• mixing of salt in water is a change that can be reversed by heating and melting of salt.

• mixing of salt in water is a change that cannot be reversed.

• mixing of salt in water is a permanent change.

• mixing of salt in water is a change that can be reversed by evaporation.

Rolling of chapati and baking of chapati are the changes that

• cannot be reversed and can be reversed, respectively.

• can be reversed and cannot be reversed, respectively.

• cannot be reversed.

• can be reversed.

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

• expands and fits onto the wooden wheel.

• contracts and fits onto the wooden wheel.

• no change in the size takes place.

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

Which of the following is a physical change?

• Melting of wax

• Burning of candle

• Combustion of magnesium ribbon

• Rusting of iron

Which of the following is a chemical change?

• Twinkling of stars

• Cooking of vegetables

• Cutting of fruits

• Boiling of water

A chemical change may involve

• any or all of these changes

• evolution of gas only

• change in temperature only

• change in colour only