Oxidation number is a formal charge assigned to an atom assuming all bonds are ionic, and the algebraic sum of oxidation numbers in a neutral molecule must equal zero. In KMnO_4, potassium contributes +1 and each of the four oxygen atoms contributes -2, giving a total of -8 from oxygen. Let the oxidation state of manganese be x. Then +1 + x + (-8) = 0, so x = +7. Manganese therefore achieves its maximum oxidation state, matching its group position, which is why permanganate is such a strong oxidising agent. Option +2 corresponds to the Mn^2+ ion formed when permanganate is reduced in acidic medium, not to KMnO_4 itself. Option +4 corresponds to MnO_2, the product in neutral or faintly alkaline medium. Option +6 corresponds to the manganate ion MnO_4^2-. This is a standard NCERT application of oxidation-number rules. Plausibility check: +7 is the highest possible for a Group 7 element, consistent with manganese using all its valence electrons.