Question

Which Of These Is An Indication That A Chemical Reaction Has Occurred?

Answer 1

Answer:

Correct option is D. Formation Of A Gas

Explanation

The main indication of chemical is that new substances are formed which have different composition than reactant.

Freezing of a substance: 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.

Melting of a substance: 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.

Boiling of a substance: 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.

Formation of gas:

In this case, chemical reaction take place. In chemical reactions, new substance are formed whose composition is different from reactants.

Answer 2

The correct option is D.

A chemical change is a type of change in which a new substance is formed and which is always irreversible. Chemical changes involves the breaking and forming of bonds and the original composition of the substances involved are usually altered. The indicators that show that a chemical change has occur include: change in temperature, change in colour, formation of precipitate and formation of gas bubbles.