If $Q$ is the magnitude of charge and $r$ is the distance between the centres of positive and negative charges,then the dipole moment $(\mu)$ is given by:

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.
$(1)$ $BeCl_2, CO_2, BCl_3, CHCl_3$
$(2)$ $SO_2, C_6H_5Cl, H_2Se, BrF_5$
$(3)$ $BF_3, O_3, SF_6, XeF_6$
$(4)$ $NO_2, NH_3, POCl_3, CH_3Cl$

The compound of xenon with zero dipole moment is

Which of the following has the lowest dipole moment?

The dipole moment of $o-$,$p-$ and $m-$dichlorobenzene will be in the order:

$H_2O$ is dipolar,whereas $BeF_2$ is not. It is because