Balance the following equation is alkaline medium
` Zn(s) = N_(3)^(-) (aq) rarr Zn^(2+) (aq.) + NH_(4)^(+) (aq)`.
Strategy : Follow the seven-step procedure, one step at a time.

Explanation

Step 1: Write the sleletal ionic equation
` Zn(s) + NO_3^(-)(aq) rarr Zn^(2+) (aq) + NH_4^(+) (aq)`
Step 2: Assingn oxidation number to all the atoms :
`overset (0) (Z)n(s) + overset(+5-2) (NO_(3)^(-)) (aq.) rarr overset (+2)(Zn^(2+)) (aq.) + overset(-3+1)(NH_(4)^(+))(aq.)`
The oxidation number of Zn increases from 0 to `+2` while the oxidation number of N drecease from ` +5 ` to ` -3`
Step 3: Idenify oxidizing and reducing agents:
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Zn is the reducing agent as it is oxidized while ` NO_(3)^(-)` is the oxidizing agent as it is reduced . Since there is only one Zn atom on either side. the total increase in the oxidation number of Zn is of two units. Since there is only one N atom on either side, the total decrease in the oxdation number of N is of eight units.
Step 4: Make the total inceease and decrease in oxidation numbers equal by multiplying Zn (reducing agent ) by 4, Also multiply `Zn^(2+)` by 4 to balance `Zn` atoms . (Step 5)
`underset("0 charge")(4Zn(s)) + underset("1- charge")(NO_3^(-) (aq.))rarr underset(4(2+)=8+" charge")(4 Zn^(2+) (aq.)) + underset("1+ charge")(NH_4^+(aq.))`
Step 6: Balance the ionic charges on both the sides by adding ` OH^(-)` ions as the reaction is carried out in basic condition. On the left side, there is ` 1-` charge due fo ` NO_3^(-)` ion but on the right side, there are ` 9+` charges due to four `Zn^(2+)` ions and one ` NH_4^+` ion. Add `10 OH^(-)` ions on the left to make ionic charges equal
`4 Zn(s) + NO_3^(-)(aq.) rarr 4Zn^(2+) (aq.) + NH_4^(+) (aq.) + 10OH^(-) (aq.)`
Step 7 : Finally balance H and O atoms by adding ` H_(2)O` molecules. There are zero H atoms and three O atoms on the left side. There are ` 14 H` atoms and ` 10 O` atoms on the left side. Thus, add `7H_(2)O` mol- ecules on the left side to achieve the balanced redox reaction : ltbtgt `4Zn(s) + NO_3^(-) (aq.) +7H_(2)O rarr 4 Zn^(2+) (aq.) + NH_4^(+)(aq.) + 10OH^(-) (aq)`.