Which bond angle $\mathrm{\theta }$ would result in the maximum dipole moment for the triatomic molecule, ${\mathrm{XY}}_2$ shown below ?

The dipole moment of   is $1.5 \mathrm{D}$. The dipole moment of

For which of the following molecules, significant $\mathrm{\mu }\ne 0$?

Among the following species, identify the isostructural pairs

${\mathrm{NF}}_3 , {{\mathrm{NO}}_3}^{-}, {\mathrm{BF}}_3 , {\mathrm{H}}_3{\mathrm{O}}^{+} , {\mathrm{HN}}_3$