Answer:
They all have 7 valence electrons on it's outer shell.
When we start heating to the given liquid the molecules absorbed energy and the average kinetic energy of each molecues present in liquid increased.
As the kinetic energy of molecules increases the molecules started to moves and the atraction force among the molecules decreased as a result the volume of liquid increased.
Hence option D correct explanation for given liquid.
D. When the heat was increased the liquid molecules expanded and increased in volume
Bromine because they are both in Group 17, which means they have the same number of valence electrons