What are the possible oxidation numbers of an element if its atomic number is 17?
-1 and 7
-1 and 6
-3 and 5
-2 and 6
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The element with atomic number 17 is chlorine (Cl).
Chlorine can exhibit a variety of oxidation states, the most common being:
-1 (as in chloride, Cl⁻ — its most stable and common oxidation state)
+1, +3, +5, and +7 (in compounds like ClO⁻, ClO₂⁻, ClO₃⁻, ClO₄⁻ respectively)
So, the possible oxidation numbers of chlorine include -1 and +7.
Correct answer: A. -1 and 7
If the options had -1 and -7 instead of -1 and 7, then none of the options would be correct — because chlorine does not exhibit an oxidation state of -7.
The lowest oxidation state chlorine can have is -1, and it never goes as low as -7. In fact, no known element has an oxidation state of -7, because that would mean it gains seven electrons, which is highly unstable and unrealistic due to energy constraints.
So, if the only option was -1 and -7, and +7 wasn't among the choices, then the correct answer would be:
> None of the above is correct — because chlorine’s oxidation states include -1 and positive values up to +7, not -7.
