MCAT General Chemistry Question 158: Answer and Explanation
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Question: 158
8. During the assigning of oxidation numbers, which of the following elements would most likely be determined last?
- A. Ar
- B. F
- C. Sr
- D. Ir
Correct Answer: D
Explanation:
When assigning oxidation numbers, one starts with elements of known oxidation state first, and determines the oxidation state of the other elements by deduction. As a noble gas, argon, choice (A), will always have an oxidation state of 0. As a group VIIA element, fluorine, choice (B), will have an oxidation state of 0 (by itself) or -1 (in a compound). As a group IIA element, strontium, choice (C), will have an oxidation state of 0 (by itself) or +2 (in a compound). Like most transition metals, iridium, choice (D), can have various oxidation states, ranging from -3 to +8. Therefore, one would have to determine the oxidation states of other atoms in an iridium-containing compound to determine iridium's oxidation number.