Which of the following has the lowest dipole moment?

"Dipole moment is a vector quantity." What does this mean? How is it represented?

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 standard molar enthalpy of vaporisation $(\Delta_{vap}H^{\circ})$ of $A, B$ and $C$ liquids is $23.3, 41$ and $29 \ kJ \ mol^{-1}$ respectively. The correct order of dipole-dipole attractive forces in these liquids is

Identify the molecule with the highest dipole moment from the following:

Which of the following bonds is the most polar?