Which of the following statements about the halides of group 15 elements are correct?

ASolid $PCl X_{5}$ consists of $[PCl X_{4}] X^{+}$ and $[PCl X_{6}] X^{-}$ ions.
BBismuth forms the pentahalide $BiF X_{5}$ but not $BiCl X_{5}$ .
C $NCl X_{5}$ is formed when $NCl X_{3}$ is treated with excess $Cl X_{2}$ .
D $PF X_{5}$ molecules have a trigonal bipyramidal geometry.

Answer: A, B, D

PCl X_{5}

is ionic in the solid state (

[PCl X_{4}] X^{+} [PCl X_{6}] X^{-}

);

PF X_{5}

is trigonal bipyramidal (

s p^{3} d

). Nitrogen has no d orbitals, so

NCl X_{5}

does not exist. Of the Bi pentahalides only

BiF X_{5}

is known (the strongly oxidising Bi(V) would oxidise chloride). Correct: A, B, D.