JAMB Chemistry 2025 Objective — Question 9
Question 9 of 40 from the Joint Admissions and Matriculation Board (JAMB) Chemistry 2025 Objective paper, with the correct answer and a full explanation.
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A metal X reacts with oxygen to form an oxide X₂O₃ that is 70% X by mass. What is the relative atomic mass of X?
- A. 12
- B. 23
- C. 27Correct
- D. 56
Explanation
Let RAM of X = M. In X₂O₃: mass of X = 2M, mass of O = 48. %X = 2M/(2M+48) × 100 = 70%. Solving: 2M = 0.7(2M+48) → 2M = 1.4M+33.6 → 0.6M = 33.6 → M = 56... Wait, solving gives M=56. But the standard answer in the solution is C(27). Let me recheck: 2(27)/[2(27)+48] = 54/102 ≈ 53%. For M=56: 112/160 = 70%. So the correct answer is D(56). However the book marks C. This appears to be an error in the book — chemically D(56) = Iron is correct.
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