Which one of the following ions is not tetrahedral  in shape?

• A

  ${\mathrm{NH}}_4^{+}$

• B

  ${\mathrm{BF}}_4^{-}$

• C

  ${\left[\mathrm{Cu}{\left({\mathrm{NH}}_3\right)}_4\right]}^{2+}$

• D

  ${\left[{\mathrm{NiCl}}_4\right]}^{2-}$