Question

Group – 2 element (A) when reacts with group – 15 element (X), the general formula of the compound formed is:

• A. \(A_3X_2\)
• B. \(A_3X\)
• C. \(A_2X_3\)
• D. \(AX_2\)

Hint:

For ionic compounds, always balance total positive and negative charges using the criss-cross method to obtain the correct formula.

Answer 1

The Correct Option is A

Step 1: Character of combining elements.
Group 2 alkaline earth metal A forms A²⁺ cations; Group 15 non-metal X forms X³⁻ anions.

Step 2: Recognizing valencies.
A has a valency of 2, X has a valency of 3, requiring balanced positive and negative charges.

Step 3: Employing the criss-cross technique.
Swapping the valencies gives the subscript ratio: A gets 3, X gets 2, yielding A₃X₂.

Step 4: Charge neutrality check.
Total positive charge = 3×(+2) = +6; total negative charge = 2×(-3) = -6; they cancel perfectly.

Step 5: Final formula determination.
The stable empirical formula satisfying ionic charge balance is A₃X₂.