Which of the following species has tetrahedral geometry?

• Correct answer
  A

  $\mathrm{BH}_4^{-}$
• B

  $\mathrm{NH}_2^{-}$
• C

  $\mathrm{CO}_3^{2-}$
• D

  $\mathrm{H}_3 \mathrm{O}^{+}$

Solution

The central $B$ atom in $\mathrm{BH}_4^{-}$undergoes $s p^3$ hybridisation, which results in tetrahedral geometry with 4 bond pairs and 0 lone pairs of electrons.

Hence, the correct answer is option: 'A'.