You can automatically rule out CH₄ since it has no lone pairs at all around the central atom. Water has 2. Ammonia is the only Lewis structure that contains one lone pair.
Due to heat , the kinetic energy of the atoms in the substance increases due to which they start vibrating vigorously and the inter-molecular attraction decreases and the substance increases in volume. For example, on boiling water...heat energy imparted makes the volume increase and finally turn into steam or water vapour in air.(The inter-molecular space in air is more than that in water.)
