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

The arrow is between MnO2-->Mn^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.

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

To determine the coefficient of H+ that balances the atoms in the given half-reaction, you need to make sure that the number of hydrogen (H) atoms on both sides of the equation is equal.

The half-reaction given is:

H+ + MnO2 -> Mn2+ + H2O

On the left side of the arrow, there is only one hydrogen atom, while on the right side, there are two hydrogen atoms.

To balance the hydrogen (H) atoms, you need to add a coefficient of 2 in front of H+ on the left side:

2H+ + MnO2 -> Mn2+ + H2O

Now, there are two hydrogen atoms on both sides of the equation, and the equation is balanced.

Looking at the answer choices, you are correct. The coefficient of H+ that balances the atoms in the half-reaction is B. 2.