Which of the following compounds is polar?

Which of the following is polar?

Although both $CO_{2}$ and $H_{2}O$ are triatomic molecules,the shape of $H_{2}O$ molecule is bent while that of $CO_{2}$ is linear. Explain this on the basis of dipole moment.

Each of the following options contains a set of four molecules. Identify the option$(s)$ where all four molecules possess a permanent dipole moment at room temperature.
$(1)$ $BeCl_2, CO_2, BCl_3, CHCl_3$
$(2)$ $SO_2, C_6H_5Cl, H_2Se, BrF_5$
$(3)$ $BF_3, O_3, SF_6, XeF_6$
$(4)$ $NO_2, NH_3, POCl_3, CH_3Cl$

Choose the polar molecule from the following:

Explain why $BeH_{2}$ molecule has a zero dipole moment although the $Be-H$ bonds are polar.