Here, the hybridisation of $CO _2$ is $sp$ whereas hybridisation of $H _2 CO _3$ is $sp ^2$, thus, hybridation changes

$(B)\,H _3 BO _3+ OH ^{-} \longrightarrow\left[ B ( OH )_4\right]^{-}$

Here, the hybridation of $B$ changes from $s p^3$ to $s p^3$

$(C) \,BF _3+ NH _3 \longrightarrow BF _3^{-} NH _4^{+}$

Here, the hybridation $N$ doesn't change.