Ionic Compound Ratio Matches Ion Charges

Steps:

• Determine charges: X (cation) loses electrons; Y (anion) gains them.
• For 1:2 ratio (XY₂), X must have +2 charge, Y -1 charge to balance.
• Check each option's ions and formula.
• Verify only one fits 1 X to 2 Y with X as positive ion.

Why A is correct:

• Calcium forms Ca²⁺ (+2); chlorine forms Cl⁻ (-1); formula CaCl₂ requires 1 Ca and 2 Cl for charge neutrality.

Why the others are wrong:

• B: Calcium (Ca²⁺) and oxygen (O²⁻) form CaO (1:1 ratio).
• C: Sodium (Na⁺) and chlorine (Cl⁻) form NaCl (1:1 ratio).
• D: Sodium (Na⁺) and oxygen (O²⁻) form Na₂O (2:1 ratio).

Final answer: A