Which is true about ${\mathrm{NH}}_2^{-},{\mathrm{NH}}_3,{\mathrm{NH}}_4^{+}?$

For ${\mathrm{NH}}_2^{-},{\mathrm{NH}}_3,{\mathrm{NH}}_4^{+}$Molecular geometry (i.e., shape) is different.

(NH2-)azanide ion has bent molecular geometry and tetrahedral electronic structure, it is having two lone pairs. A central Nitrogen atom is attached to two hydrogen atoms to form the NH2- ion. Nitrogen and hydrogen can only form single bonds with one another.

NH3 molecule has the triangular pyramid or deformed tetrahedral structure.

The core nitrogen atom of ammonium, NH4+, is surrounded by four hydrogen atoms. Its molecular form and electron geometry are both tetrahedral.

Hence,for ${\mathrm{NH}}_2^{-},{\mathrm{NH}}_3,{\mathrm{NH}}_4^{+}$Molecular geometry (i.e., shape) is different.