Indians are a hard-working race.

Identify the collective noun or nouns?give reason.

From your doubt, it is clear that the concept of collective noun is not clear to you. Please do not confuse the plural form of nouns with collective form of nouns. However, the human race can be explained as a collective noun. Here is an explanation of collective noun that would help you understand the concept better:

A collective noun is a word that talks about the people and things spoken of as a group and not as single. For example:

The Indian army fought bravely. 

The committee decided to organise an inter-school tournament. 

Hope this helps!