Identify the noun:

Sita is an architect.

Option C is the correct answer. Any person, place, animal, or thing's name is a Noun. Six categories of nouns exist. There are six types of nouns: Proper, Common, Collective, Abstract, Countable, and Uncountable. 
The words given in this statement are "proper noun"(Sita) and "common noun"(architect). The definite name of a person, place, animal, or thing is a Proper noun. A Common noun is any name for a person, place, animal, or item.