Assign reason for the following :
(i) Ammonia is soluble in water while phosphine is not
(ii) `B_(2)` is paramagnetic while `C_(2)` is not.

Explanation

(i) Ammonia `(NH_(3))` is involved in intermolecular hydrogen bonding with the molecules of water `(H_(2)O).`

Energy relased during attraction helps in dissolving ammonia in water to from ammoniu hydroxide `(NH_(4)OH).` In phosphine `(PH_(3)),` P-H bond is almost non-polar because both P and H atoms have the same electronegativily (2.1). There is on hydrogen bonding in the molecules of phosphine and water and therefore, phosphine does not dissolce in water.
(ii) The molecular orbital electronic configuratioln both `B_(2)and C_(2)` are given :
`" "B_(2): [sigma_(1s)]^(2)[sigma_(2s)]^(2)[sigma_(2s)^(**)]^(2)[pi_(2py)]^(1)[pi_(2py)]^(1)`
`" "C_(2): [sigma_(1s)]^(2)[sigma_(2s)]^(2)[sigma_(2s)^(**)]^(2)[pi_(2py)]^(2)[pi_(2py)]^(2)`
Since `B_(2)` has two unpaired electrons, it is paramagnetic in nature. `C_(2)` is diamagnetic in nature as it has no unpaired electron present in the molecular orbitals.