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Engineering Exams RRB-JE CMA (Chemical and Metallurgical Assistant) General Abilities 2025 22.04.25 Paper-2 Shift-2 Easy +1 -0.33
Identify the correct formula for the compound formed between Mg²⁺ and PO₄³⁻ ions.
Correct Answer: B. Mg₃(PO₄)₂
Explanation: To form a neutral ionic compound between magnesium (Mg²⁺) and phosphate (PO₄³⁻), the total positive and negative charges must balance. Magnesium has a +2 charge, while the phosphate polyatomic ion has a -3 charge. The lowest common multiple of 2 and 3 is 6. To achieve a net charge of zero, three magnesium ions (totaling +6) are required to pair with two phosphate ions (totaling -6). Therefore, the correct chemical formula is Mg₃(PO₄)₂, where the subscripts indicate the ratio of ions needed for electrical neutrality.
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