Question

What is the nature of this chlorine ion?

Answer 1

As chlorine has seven electrons in its outer most shell so to complete its octet it has to gain an electron and when it gain an electron it will become an anion that is negatively charged
 so in my opinion and what a conclude is that the option B is correct for the above statement

Answer 2

The chlorine anion is a Lewis base.
The chlorine anion is a donor of electronic pair:

Cl⁻ + H⁺ → HCl