Which of the following is not tetrahedral?

1) ${\mathrm{BF}}_4^{-}$

H = 1/2 [V + M - C + A]

= 1/2 [3 + 4 - 0 + 1]

= 1/2 [8] = 4 ⇒ sp³ ⇒ Tetrahedral

2) ${\mathrm{NH}}_4^{+}$

H = 1/2 [5 + 4 - 1 + 0]

= 8/2 = 4 ⇒ sp³ ⇒ Tetrahedral

3) ${\mathrm{CO}}_3^{2-}$

H = 1/2 [4 + 0 - 0 + 2]

= 6/2 = 3 ⇒ sp² ⇒ Trigonal planar

4) ${\mathrm{SO}}_4^{2-}$ 

H = 1/2 [6 + 0 - 0 + 2]

= 8/2 = 4 ⇒ sp³ ⇒  Tetrahedral.