We are being asked to balance the given redox reaction occurring in a basic solution.
When balancing redox reactions under basic conditions, we will follow the following steps.
Step 1. Separate the whole reaction into half-reactions
Step 2. Balance the non-hydrogen and non-oxygen elements first
Step 3. Balance oxygen by adding H2O to the side that needs oxygen (1 O: 1 H2O)
Step 4. Balance hydrogen by adding H+ to the side that needs hydrogen (1 H: 1 H+)
Step 5. Balance the charges: add electrons to the more positive side (or less negative side)
Step 6. Balance electrons on the two half-reactions
Step 7. Get the overall reaction by adding the two reaction
Step 8. Balance remaining H+ by adding an equal amount of OH- ions to both sides
Step 9. H+(aq) will combine with OH-(aq) to form H2O(l)
Step 10. Cancel out common species.
Balance the redox reaction under basic condition:
NO2−(aq) + Al(s) → NH3(g) + AlO2−(aq)