Arrange the following in order of decreasing bond angle.
a. `CO_(2), H_(2)O, CH_(4)`
b. `SO_(4)^(2-), SO_(3)^(2-)`

Explanation

a. `CO_(2) gt CH_(4) gt H_(2)O`
i. `CO_(2)` is `sp` hybridised `(overset(..)underset(..)(O)=C=overset(..)(O): )` and is linear, so the bond angle is `180^(@)`.
ii. `CH_(4)` is `sp^(3)` hybridised and is tetrahedral so the bond angle is `109.5^(@)`.
iii. `H_(2)O` is also `sp^(3)` hybridised, but due to two lone pairs it is bent or V-shaped, so the bond angle is `104.5^(@)`.
b. `SO_(4)^(2-) gt SO_(3)^(2-)`
i. `SO_(4)^(2-)` is `sp^(3)` hybridised `(O^(ɵ)= underset(O^(ɵ))underset(||)overset(O)overset(||)(S)-O^(ɵ))`, and is tetrahedral so the bond angle is `109.5^(@)`.
ii. `SO_(3)^(2-)` is also `sp^(3)` hybridised `(O^(ɵ)- underset(..)overset(O)overset(||)(S)-O^(ɵ))`, due to one angle pair, it is pyramidal in shape, so the bond angle is `107^(@)`.