Which among the following is not haloalkyne?

Which isomer of $\mathrm{C}_4 \mathrm{H}_9 \mathrm{OH}$ has highest boiling point?

A buffer solution contains equal concentrations of weak acid and its salt with strong base. Calculate pH of buffer solution if dissociation constant of weak acid is $1.8 \times 10^{-5}$.

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.