Chemistry - PERIODIC TABLE Question with Solution | TestHub

(A) is correct: $A$ is two positions to the left of $C$ in the same period; thus, adding two electrons to $A$ ($A^{2-}$) makes it isoelectronic with $C$.

(B) is correct: $Q$ is in group $n$, $P$ is in $n-1$, and $O$ is in $n+1$. Therefore, $P^{-}$ and $O^{+}$ both achieve the same valence electron count as $Q$.

(D) is correct: Ionization Energy ($I{E}_1$) increases up a group and across a period. $C$ (top-right) has the highest $I{E}_1$ and $M$ (bottom-left) has the lowest, making their difference the maximum.

(C) is incorrect: The atomic number difference between $P$ and $A$ (vertical, usually 8) is not equal to the difference between $Q$ and $R$ (horizontal, 1).