Question

Identify the sentence that uses the possessive pronoun correctly.
A. That sweater is hers'.
B. That sweater is her's.
C. That sweater is hers.
D. That sweater is hers's.

Answer 1

I believe the answer is B.

Answer 2

The correct answer is C.
Hers is a possessive pronoun. Itself, it already shows possession, that´s why the apostrophe isn´t necessary. It´s a common misunderstanding. 
Hope you understood!