(a, b, c, d)

Because of diagonal relationship both have same electronegativity (Be = 1.5 & Al = 1.5).

Beryllium hydroxide dissolves in excess of alkali to give a beryllate ion, [ Be(OH)4]2– just as aluminium hydroxide gives aluminate ion, [Al(OH)4]– and salt with acids.

The ionic radius of Be2+ is estimated to be 45 pm; the charge/radius ratio is nearly the same as that of the Al3+ ion (the charge per unit area is nearly similar, Be2+ = 2.36 and Al3+ = 2.50).

The chlorides of both beryllium and aluminium have Cl– bridged chloride structure in vapour phase