Question

This is ______ unique coin

Answer 1

Hey mate !!

This is a unique coin.

Hope this helps ^-^

Answer 2

This is a unique coin .
Why a :
The article 'a' is used up here becoz the coin we are talking about here is not well defined , that is , which coin ? Where is the coin from ? Nothing is described here not about the place of where it is nor about which type of coin . Thus , hereby the article 'a' is used up here .