Question

Which statement about the ammonium ion,$N{H_4}^{+}$ is correct?
(A)All bond angles are ${107}^{\circ }$
(B)Ammonium ions are formed when ammonia behaves as an acid
(C)Ammonium ions are unreactive when heated with NaOH(aq)
(D)The bonds are all the same length

Answer 1

Hint: Ammonium ions have tetrahedral shape, and ammonia have a lone pair to donate to form ammonium ion, also ammonium ions have no lone pair present to distort the normal tetrahedral angle.

Complete answer:
We will start with every statement one by one, looking whether it is right or wrong.
Considering option (A) , all bond angles are ${107}^{\circ }$. This statement is not correct because the ammonium ion has four bond pairs, which makes the shape of the molecule tetrahedral, and tetrahedral molecules have a bond angle of ${109.5}^{\circ }$. There is no lone pair on nitrogen left, to decrease the bond angle of the bond pair. The bond angle of ammonium ion is ${109.5}^{\circ }$.
Considering option (B), Ammonium ions are formed when ammonia behaves as an acid. This statement is not correct, because ammonium ion is formed when ammonia takes up a proton from the medium, so according to this, ammonia acts as base. Base accepts the proton, and acid releases the proton.
Considering option (C), Ammonium ions are unreactive when heated with NaOH(aq). This statement is not correct, because ammonia in reaction with NaOH gives ammonia and water.
     $$N{H}^{+}+O{H}^{-}\to N{H}_3+H_{2}O$$
Considering option (D), The bonds are all the same length. This statement is correct because all the bonds are $s{p}^3$hybridized.

Therefore, the correct answer is (D) option.

Note: Ammonia acts as base, it is accepting hydrogen ions from the water. Ammonium ion is its conjugate acid,it can release hydrogen ion to reform back to ammonia.Ammonia is a weak base and ammonium ion is a weak acid. Although, every weak base has a strong conjugate acid , but that may not be necessary in every case.