Correct Answer - B
Due to ineffective shielding of 3d-orbitals , the effective nuclear charge of Ga is greater in magnitude than of Al. As a result, atomic radii of Fa is lower than that of Al. The atomic radii of remaining element increases regularly as we move down the group from ln to Tl. Thus, atomic radii of the four elements from Al to Tl increase in the order : `Ga lt Al lt In lt Tl`, i.e., option (b) is correct.
