Question

Manganese has the oxidation number of +5 in ______ . .
(A) [MnF6]3– (C) [MnO4]2–
(B) Mn2O7 (D) [Mn(CN)6]–

Answer 1

Take a.
F is -1. 6 of them makes -6. We want to leave a -3 charge on the ion; therefore, Mn must be +3. +3 and -6 = +3.

b. Mn2O7. O is -2. Seven of them makes -14.
14/2 = +7 each for Mn. Check it. +14 for 2 Mn + (-14) for 7 O atoms = 0.

c. MnO4^-. O is -2. Four of them make -8. We want to leave a -1 charge on the ion; therefore, Mn must be +7. Check it. +7 + (-8) = -1 charge on the ion.

d. Mn(CN)6^-1.
CN is -1, six of them makes -6. We want to leave a -1 charge on the ion; therefore, Mn must be +5.
Check it. Mn = +5 + (-6 for CN) = -1 charge on the ion.