JEE Chemistry 2025 Question with Solution

Given: The elements are Li, Na, Be, Mg, B, and Al.

Find: The type of oxide formed by the element having the least atomic radius.

Across a period, atomic radius decreases from left to right because effective nuclear charge increases. Also, atomic radius increases down a group.

Among the given elements, B has the smallest atomic radius.

Boron forms boron trioxide:

$$B_2O_3$$

So, the general type of oxide is:

$$A_2O_3$$

Therefore, the correct option is A.

Given: The elements are Li, Na, Be, Mg, B, and Al.

Find: Which oxide formula corresponds to the element with the least atomic radius.

Step 1: Use periodic trend. Atomic radius decreases across a period from left to right and increases down a group.

Step 2: Compare the listed elements.

• Li, Be, B are in the second period.
• Na, Mg, Al are in the third period.

Elements in the third period are generally larger than the corresponding elements in the second period. In the second period, radius decreases as:

$$Li > Be > B$$

Hence, B has the least atomic radius among all the given elements.

Step 3: Write the oxide of boron. Boron forms:

$$B_2O_3$$

Thus, the oxide type is:

$$A_2O_3$$

Therefore, the correct option is A.

The first extracted solution statement mentions Al, but the detailed working shows that B has the smallest atomic radius. The option selected remains A because both B_2O_3 and the listed oxide type correspond to $A_2O_3$.