Question

A chemical change may involve
(A) Change in colour only
(B) Change in temperature only
(C) Evolution of gas only
(D) Any or all of above

Answer 1

Hint: Changes are of 2 types-physical and chemical. Physical changes are temporary changes which do not involve change in composition for example ice changing into water on heating. Chemical changes involve 2 or more substances combining together to form new substances and are permanent changes. Chemical change is responsible for production of new substances for example mixing of acid and base.

Complete answer:
In chemical change we will consider several chemical reactions around us .These reactions may be reversible or irreversible, Endothermic (absorb heat) or Exothermic (release heat), produce sound, produce precipitate, light or any other radiations be absorbed or released, a change in smell or new smell may be produced, a change is color is produced, temperature change takes place etc.
Now let us take a close look at all the options-
(A) Change in color:
An example of such reaction that involves color change is-
$Fe + CuS{O_{4}} \to FeS{O_4} + Cu$
When Iron reacts with Copper sulphate it forms Copper and Ferrous Sulphate. The color changes from blue (of Copper Sulphate) to green (of Ferrous Sulphate) in the reaction.
(B) Change in temperature:
An example of such reaction that involves change in temperature is-
$CaO + {H_2}O \to Ca{(OH)_2}$
When Quicklime reacts with water it forms slaked lime. In this reaction heat is released, thus causing temperature change in the reaction.
(C)Evolution of gas-
An example of such reaction that involves Evolution of gas-
$Zn + {H_2}S{O_4} \to ZnS{O_4} + {H_2}$
When Zinc reacts with Sulphuric Acid to form Zinc Sulphate and Hydrogen gas is evolved.
As all of the options are correct hence Option (D) is correct.

Note:
It is very interesting to note that digestion of food is an example of physical as well as chemical change. It is a physical change since it involves breaking of large molecules into small in the mouth and it is a chemical change since in the stomach and intestine several enzymes (or chemicals) are released that result in several chemical reactions.