Previous Year NEET Question- Chemical Bonds L-4

Question: Amongst the following, the total number of species NOT having eight electrons around central atom in its outer most shell, is $\mathrm{NH}_3, \mathrm{AlCl}_3, \mathrm{BeCl}_2, \mathrm{CCl}_4, \mathrm{PCl}_5$ :#

2

4

1

3

Answer: 3#

Solution:#

SiCl$_4$, NH$_4^{+}$, SO$_4^{2-}$ and PO$_4^{3-}$ ions are the examples of molecules/ions which are of $AB_4$ type and have tetrahedral structures. SCl$_4$ is $AB_4$ (lone pair) type species. Although the arrangement of five $sp^3d$ hybrid orbitals in space is trigonal bipyramidal, due to the presence of one lone pair of electrons in the equatorial hybrid orbital, the shape of $AB_4$ (lone pair) species gets distorted and becomes see-saw.