<u><em>Answer:</em></u>
Correct option is D. Formation Of A Gas
<u><em>Explanation</em></u>
The main indication of chemical is that new substances are formed which have different composition than reactant.
<u><em>Freezing of a substance: </em></u>As in this case composition remained same, so we cant say, chemical reaction is take place, like when water freezes, it composition is same as water , so it is only its physical properties, not chemical.
<u><em>Melting of a substance:</em></u> As in this case composition remained same, so we cant say, chemical reaction is take place, like when ice melts, composition of water remained same , so it its physical properties, not chemical.
<u><em>Boiling of a substance:</em></u> As in this case composition remained same, so we cant say, chemical reaction is take place, like when water boils and become vapors, composition of water and vapors remained same , so it its physical properties, not chemical properties which show its chemical reaction.
<u><em>Formation of gas:</em></u>
In this case, chemical reaction take place. In chemical reactions, new substance are formed whose composition is different from reactants.
