Assertion: A reaction in which two or more products are formed by a single reactant is called decomposition reaction.

Reason: When decomposition is not carried out by heating it is known as thermal decomposition.

Choose the correct option out of the following.

Assertion is correct but reason is incorrect.

The correct answer is option 3. Assertion is correct but reason is incorrect.

The assertion that a reaction in which two or more products are formed by a single reactant is called a decomposition reaction is correct. In a decomposition reaction, a compound breaks down into two or more simpler substances. However, it doesn't necessarily have to involve a single reactant; it can also involve two or more reactants.

The reason provided, that when decomposition is not carried out by heating, it is known as thermal decomposition, is not accurate. Thermal decomposition refers specifically to decomposition reactions that occur as a result of heating. However, decomposition reactions can occur through other means as well, such as exposure to light or electricity.

Therefore, while the assertion is correct, the reason is not a correct explanation for it.