Out of Li+, Be2+ and B3+ ions, which has the smallest ionic radius and why ?

Looking at the periodic table we can see that the three cations have equal number of electron (after removing electrons from the neutral atoms, B, Be and Li). However, B³⁺ will have the smallest radius followed by Be²⁺ . Li⁺ will have the largest ionic radius among the three. The smallest radius of B³⁺ is due to the fact that the high nuclear charge of +3 would be pulling the electron density towards itself more strongly than a +2 or +1. Therefore, the electron density is contained in less space in the B³⁺ resulting in a smaller ionic radius of this cation. While the Li⁺ will be the largest because the nuclear charge on it (+1) is least out of the three. Be²⁺ will have the size in between the two cations. 

Therefore, the order of ionic radius is ​B³⁺ < Be²⁺ < Li⁺ even though the  three cations have equal no. of electrons.