# NEET Chemistry The p-Block Elements (XII) Questions Solved

BOARD

Account for the following:

(i) $N{H}_{3}$ is a stronger base than $P{H}_{3}.$

(ii) Sulphur has a greater tendency for catenation than oxygen.

(iii) Bond dissociation energy of ${F}_{2}$ is less than that of $C{l}_{2}.$

(i) Since both P and N contain lone pairs of electrons but due to small size and high electronegativity of Nitrogen in $N{H}_{3},$ the electron density is much higher than $P{H}_{3},$ therefore it can easily donate electrons and acts as strong Lewis base than $P{H}_{3}.$

(ii) The greater catenation tendency of sulphur is due to two reasons :

(a) The lone pair of electrons feels more repulsion in O-O bond than S-S bond due to its small size and thus S-S forms strong bond.

(b) As the size of atom increases down the group from O-PO, the strength of bond increases and therefore catenation tendency also increases.

(iii) Due to smaller size of F than Cl as a result of which electron-electron repulsions between the lone pairs of electrons are very large than that of Cl, hence bond dissociation energy of ${F}_{2}$ is less than that of $C{l}_{2}.$

Difficulty Level:

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