If X is a group lll element, its oxide would be represented as

Analyze the question: A Group III element (like Al, B) is asked to form an oxide. We need the correct formula.

Concept: Group III elements have 3 valence electrons, so they lose 3 electrons to form X³⁺. Oxygen is in Group VI, has 6 valence electrons, and gains 2 electrons to form O²⁻. To write the formula, we balance the charges using the criss-cross method.

Solution:

1. Ion of X: X³⁺
2. Ion of oxygen: O²⁻
3. Criss-cross the charges: the 3 from X goes to O, and the 2 from O goes to X.

X₂O₃

4. Check the charge balance: 2(+3) = +6 and 3(−2) = −6, so the total is 0.

Comparing with the options:

• A. X₃O₂ gives +9 and −4, which is not balanced.
• B. X₃O gives +9 and −2, which is not balanced.
• C. X₂O₃ gives +6 and −6, which is balanced.
• D. XO₃ gives +3 and −6, which is not balanced.

Correct answer: C. X₂O₃

A real example is aluminium oxide, Al₂O₃.

Tip: For any oxide, criss-cross the valencies. Group III (valency 3) with oxygen (valency 2) always gives X₂O₃. Group I gives X₂O, Group II gives XO, and Group IV gives XO₂.