JEE Main · 2011 · 10 Apr 2011 · Offline · p-Block Elements

Boron cannot form which one of the following anions ?

(A) $BH_{4}^{-}$
(B) $B (OH)_{4}^{-}$
(C) $BO_{2}^{-}$
(D) $BF_{6}^{3 -}$ ✓ Correct

Answer: (D)

Solution

Boron's valence shell has only one

2 s

and three

2 p

orbitals, four in all, and no

d

orbitals to expand its octet, so it can bond to at most four groups. The ions

B H_{4}^{-}

B (OH)_{4}^{-}

and

B O_{2}^{-}

all keep boron within a coordination number of four, but

B F_{6}^{3 -}

would need six bonds around boron, which it cannot form.

JEE Main · 2011 · 10 Apr 2011 · Offline · Single correct option

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