Q 15 Obstinate and surly, the manager's attitude prevented his staff from befriending him.

The rectified sentence as given in the answers is - "The manager's obstinate and surly attitude prevented his staff from befriending him".

My question is regarding the portion in red - Since him is the objective case of pronoun he how can it refer to a possessive noun "manager's". Shouldn't "him" be replaced by "manager"?

Yes, you have spotted an instance of what we call possessive poison. As it appears in your post, "him" may not refer back to "manager's."

When I look at the answer key, though, I see "The manager's obstinate and surly attitude alienated his employees." Here the pronoun "his" correctly refers back to "the manager's." Maybe you have an earlier edition? I'm looking at the 2007 edition, and I don't have the earlier one on hand.

At any rate, your initial point is a good one. Subject and object pronouns may not have possessive nouns as antecedents.

Rey