In the reaction $BCl_3 + :PH_3 \rightarrow Cl_3B \leftarrow PH_3$,which species acts as a Lewis base?

The covalency of nitrogen in $HNO_3$ is

In $BF_3$,the $B-F$ bond length is $1.3 \ \mathring{A}$. When $BF_3$ reacts with $Me_3N$,it forms an adduct $Me_3N \to BF_3$. In this adduct,the $B-F$ bond length will be ..........

In the coordinate valency:

Which of the following molecules does not have coordinate bonds?

Dative bond (coordinate bond) is present in: