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Option A Explanation:- Between NH3 and PH3:- The electronegativity of Nitrogen is much more than phosphorous. Thus the N-H bonds in NH3 are polar and the Hydrogen atoms of NH3 acquire a partially positive charge while the H atoms of PH3 remain neutral. The partially charged H atoms of NH3 repels each other and thus Bond Angle increases. While PH3 lacks this effect. Thus bond angle of NH3 is greater than PH3.
Between NH3 and H20:- In H2O there are two lone pairs of electrons whereas in NH3 there are only one lone pair of electron. In H2O, lone pair-lone pair repulsion takes place whereas in NH3 lone pair-bond pair repulsion takes place. The lone pair-lone pair repulsion is more strong than lone pair-bond pair repulsion. Thus, the bond angle in a water molecule is less than the ammonia molecule. Bond angle α1/No.of lone pair (for same hybridisation compound)
Between H20 and H2S:- As we know in both structure two bond pair and two lone pair are present and both has tetrahedral geometry. In H2O, oxygen is more electronegative, electrons of two O-H bonds are more attracted towards oxygen atom. Consequently more bond pair- bond pair repulsion take place,so bond angle get increase On the other hand in H2S, because of less electronegative character of S,less repulsion is present so angle get decrease.