How do you balance these reactions using the half-reaction method?

Question

Please balance the following reactions using the half-reaction method.

1. MnO4^- ----> MnO4^2- O2 basic

2. P ---> PH3 H2PO2^- basic

3. Zn As2O3 ----> AsH3 acidic

Answer 1

MnO4^- ----> MnO4^2- + O2 basic

4(MnO4- + 1e- -->  MnO4= )

2H2O -->  O2 + 4H+ + 4 e-

--------------------------------------...

4MnO4 + 2H2O --> 4MnO4= + O2 + 4H+

add 4 OH- to each side to neutralize the H+

4MnO4- + 2H2O + 4OH- --> 4MnO4= + O2 + 4HOH

simplify

4MnO4- + 4OH- --> 4MnO4= + O2 + 2HOH

===================

P ---> PH3 + H2PO2^-

P + 3H+ + 3e- --> PH3

P + 3H2O--> H2PO3- + 4H+ + 3e-

--------------------------------------...

2P + 3H+ + 3H2O --> PH3 + H2PO3- + 4H+

add 4 OH- to each side

2P + 3HOH + OH- + 3H2O --> PH3 + H2PO3- + 4HOH

simplify

2P + OH- + 2H2O --> PH3 + H2PO3-

=======================

Zn + As2O3 ----> AsH3

This isn't anything, not a half reaction, not the whole reaction.  It needs Zn2+ on the product side, along with some water, maybe, and some H+ on the reactant side.  BUT WAIT!!!   It's not even redox.  As is +3 in As2O3 and it's +3 in AsH3.  This one isn't ready for prime-time.