Question

Explain why $BeH_2$ molecule has a zero dipole moment although the $Be-H$ bonds are polar

Answer 1

The Lewis structure for $BeH_2$ is as follows:

There is no lone pair at the central atom $(Be)$ and there are two bond pairs. Hence, $BeH_2$ is of the type $AB_2$. It has a linear structure.

Dipole moments of each $H-Be$ bond are equal and are in opposite directions.
Therefore, they nullify each other.

Hence, $BeH_2$ molecule has zero dipole moment.