What coefficient of H+ balances the atoms in the following half-reaction?

Question

H^+ + MnO2 Mn^2+ + H2O
A.1
B.2
C.3
D.4
I think this is B...?

Answer 1

The arrow is between MnO2-->Mn^2+

Answer 2

each H gains zero electrons (from +1 to +1)

each O gains one electron(-1 to -2_

each Mn loses two electrons(+4 to +2)

so, if Mn loses two, and each O gains 1, it takes two O to absorb those electrons, so the coefficent of the H2O is 2, and the coefficent then of H+ is not B, but twice that.

Answer 3

Ya know - I originally thought D but someone else told me I was wrong...