The correct option is B 5P2H4⟶6PH3+P4H2
The unbalanced redox equation is as follows:
P2H4⟶PH3+P4H2
Balance all atoms other than H and O.
5P2H4⟶2PH3+2P4H2
The oxidation number of P changes from -2 to -3. The change in the oxidation number per P atom is 1.
Total change in the oxidation number for 2 P atoms is 2.
The oxidation number of P changes from -2 to -0.5. The change in the oxidation number per O atom is 1.5.
Total change in the oxidation number for 8 P atoms is 12.
The increase in the oxidation number is balanced with decrease in the oxidation number by changing the coefficient of P2H4 to 6 and the coefficient of PH3 to 1.
5P2H4⟶6PH3+P4H2
This is the balanced chemical equation.