The type of oxide formed by the element among $\mathrm{Li}, \mathrm{Na}, \mathrm{Be}, \mathrm{Mg}, \mathrm{B}$ and Al that has the least atomic radius is :

(A) $\mathrm{A}_{2} \mathrm{O}_{3}$

(D) $\mathrm{A}_{2} \mathrm{O}$

JEE Main · 2025 · 29 Jan 2025 · Shift 2 · s-Block Elements

The type of oxide formed by the element among

Li, Na, Be, Mg, B

and Al that has the least atomic radius is :

(A) $A_{2} O_{3}$ ✓ Correct
(B) $AO_{2}$
(C)AO
(D) $A_{2} O$

Answer: (A)

Solution

Among Li, Na, Be, Mg, B and Al, atomic radius falls across a period and rises down a group. Boron, sitting at the top-right of this set with a small size due to high effective nuclear charge for period 2, has the smallest atomic radius of the six. Boron's characteristic oxide is

B_{2} O_{3}

, an acidic oxide of the general formula type

A_{2} O_{3}

JEE Main · 2025 · 29 Jan 2025 · Shift 2 · Single correct option

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