Take ionic radii Be^2+ = 31 pm and Al^3+ = 54 pm. The ratio (charge/radius of Be^2+) : (charge/radius of Al^3+) is closest to

JEE Main levelSingle correct optionDifficulty 2 of 3sb066

Take ionic radii $Be X^{2 +}$ = 31 pm and $Al X^{3 +}$ = 54 pm. The ratio (charge/radius of $Be X^{2 +}$ ) : (charge/radius of $Al X^{3 +}$ ) is closest to

Charge/radius for Be2+ is

2/31 = 0.0645

and for Al3+ is

3/54 = 0.0556 p m^{- 1}

. The ratio is

0.0645/0.0556 = 1.16

. The two ions have similar polarising power, which underlies the diagonal relationship.