Question

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

• A. \( \text{A}_2\text{O}_3 \)
• B. \( \text{AO}_2 \)
• C. \( \text{A}_2\text{O} \)
• D. \( \text{A}_2\text{O}_4 \)

Hint:

The atomic radius decreases across a period from left to right due to an increase in nuclear charge, which pulls the electrons closer to the nucleus.

Answer 1

The Correct Option is A

The atomic radius generally decreases across a period from left to right due to increasing nuclear charge. Among the elements given (Li, Na, Be, Mg, B, Al), the atomic radius decreases as we move across the period from Li to Al. The element that forms the oxide with the least atomic radius is Al (aluminum), which forms \( \text{A}_2\text{O}_3 \).
Thus, the correct answer is \( \boxed{(1)} \).

Answer 2

Step 1: Understand the given elements.
The elements given are Li, Na, Be, Mg, B, and Al. These belong to the second and third periods of the periodic table. As we move from left to right across a period, the atomic radius decreases due to an increase in effective nuclear charge.

Step 2: Identify the element with the least atomic radius.
Among the given elements:
Li → Na → Be → Mg → B → Al
Comparing their positions in the periodic table:
- Li, Be, and B are in the 2nd period.
- Na, Mg, and Al are in the 3rd period.
Since atomic radius decreases across a period and increases down a group, **Boron (B)** has the smallest atomic radius among the given elements.

Step 3: Determine the type of oxide formed by the element.
Boron forms **boron trioxide**, \( B_2O_3 \).
The general formula of the oxide formed by elements of group 13 is \( \text{A}_2\text{O}_3 \).

Step 4: Nature of the oxide.
\( B_2O_3 \) is an acidic oxide, as boron is a metalloid. However, the question asks for the type of oxide based on the formula, not its acidic or basic nature.

Step 5: Final Answer.
The type of oxide formed by the element (boron) with the least atomic radius is:
\[ \boxed{\text{A}_2\text{O}_3} \]