$X$ melts at a low temperature and is a bad conductor of electricity in both liquid and solid states. $X$ is:

Which of the following forces is effective between noble gas atoms?

Metallic lustre is due to

The lattice enthalpy of an ionic compound is the enthalpy change when one mole of an ionic compound in its solid state dissociates into its ions in the gaseous state. It is impossible to determine it directly by experiment. Suggest and explain an indirect method to measure the lattice enthalpy of $NaCl_{(s)}$.

The type of attractive forces between a polar molecule and a non-polar molecule is

Which of the following does not conduct electricity?