If P % Q means P is the brother of Q; P ! Q means P is the father of Q and P * Q means P is the son of Q, which of the following choices shows that P is the brother of S?

We need an expression that establishes $P$ is the brother of $S$. This requires $P$ to be male, and $P$ and $S$ to share the same parentage.
Let's evaluate the options to test the relations:

* In Option (A): $P\ast Q!R\%S$
1. $P\ast Q⟹P$ is the son of $Q$.
2. $Q!R⟹Q$ is the father of $R$.
3. $R\%S⟹R$ is the brother of $S$.
Since $P$ is the son of $Q$ and $Q$ is the father of $R$ and $S$, $P,R,\text{ and }S$ are all children of $Q$. Since $P$ is a son (male), $P$ is the brother of $S$. This completely satisfies the requirement.