B, Al and Ga belong to group 13 in the periodic table and are present one below the other.
The energy levels of the atoms depend on the value of the principal quantum number n which is reflected in their valence electron configuration as represented below:
B = 2s²2p¹
Al = 3s²3p¹
Ga = 4s²4p¹
thus for B; n = 2, Al; n = 3 and Ga; n = 4
Ans: D) Aluminum has three energy levels, and gallium has four energy levels.