Q1: An ideal gas can be liquified, because

ANS:C - forces operative between its molecules are negligible.

An ideal gas can be liquefied due to the forces operative between its molecules being negligible. In the gaseous state, molecules of an ideal gas are assumed to have no volume and do not exert any intermolecular forces on each other. However, when the gas is subjected to conditions such as high pressure and low temperature, the intermolecular forces become significant, causing the gas molecules to come closer together. Eventually, at certain conditions, these intermolecular forces can cause the gas to condense into a liquid. So, the correct option is: "forces operative between its molecules are negligible."