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Q.
Boron does not form $B^{3+}$ ions whereas Al forms $Al^{3+}$ ions. This is because
The p-Block Elements
Solution:
Boron atom is smaller in size and therefore, the sum of $IE_1 + IE_2 + IE_3 (3659\, kJ\, mol^{-1})$ for B is much higher than that of $Al\, (2744\, kJ\, mol^{-1})$. Hence B does not form $B^{3+}$ ions.