Identify isoelectronic pair from following.

Which of the following elements belongs to second group and fifth period of periodic table?

Which element from following has largest atomic size as compared to other three?

If four different elements A, B, C and D having electronic configuration as $\mathrm{A}=[\mathrm{Ne}] 3 \mathrm{~s}^2 3 \mathrm{p}^4$, $B=[\mathrm{Ne}] 3 \mathrm{~s}^2 3 \mathrm{p}^5, \mathrm{C}=[\mathrm{Ar}] 3 \mathrm{~d}^{10} 4 \mathrm{~s}^2 4 \mathrm{p}^4$ and $\mathrm{D}=[\mathrm{Ar}] 3 \mathrm{~d}^{10} 4 \mathrm{~s}^2 4 \mathrm{p}^5$.

Identify the element with largest atomic radius.