Question

the pronoun in bold is not vague. select its one clear antecedent.
scientists have discovered that mercury is shrinking! in the process, its surface is wrinkling and cracking.

Explanation:

To determine the antecedent of the pronoun "its", we analyze the context. The sentence talks about Mercury shrinking, and then "its" refers to the surface of the subject that is shrinking. The subject here is Mercury, so "its" (bolded) has the clear antecedent Mercury.

Answer:

Mercury