The correct option is
B p (2), q (6), r (2), s (3)
pMnO4−(aq)+qI−+xH2O(l)→rMnO2(s)+sI2(s)+yOH−(aq)in a balanced chemical reaction number of all atoms at right side should be equal to the left side of the reaction.
Balancing a chemical reaction as:
Step 1: Assign oxidation numbers to each of the atoms in the equation and write the numbers above the atom as:
+7MnO4−(aq)+−1I−+H2O(l)→+4MnO2(s)+0I2(s)+OH−(aq)
Step 2: Identify the atoms that are oxidized and those that are reduced as:
Reduction: +7MnO4−(aq)→+4MnO2(s)
Oxidation: −1I−→0I2(s)
Step 3: oxidation-number change is:
Reduction: +7MnO4−(aq)→+4MnO2(s) Gain of 3 electron per Mn atom
Oxidation: −1I−→0I2(s): Loss of total 2 electrons
Step 4: Balance the total change in oxidation number as:
Reduction: +7MnO4−(aq)→+4MnO2(s)×2: Gain of 6 electron total
Oxidation: −1I−→0I2(s)×3: Loss of 6 electron
Step 5: Balance O atoms in reduction reaction by adding H2O and then balance H by H+ as:
2+7MnO4−(aq)+8H+→2+4MnO2(s)+4H2O
Step 6: For base catalysed reaction add OH− to both side to neutralize H+ as:
2+7MnO4−(aq)+8H++8OH−→2+4MnO2(s)+4H2O+8OH−
or, 2+7MnO4−(aq)+4H2O→2+4MnO2(s)+8OH−
Thus overall reaction is:
2+7MnO4−(aq)+6−1I−+4H2O→2+4MnO2(s)+30I2(s)+8OH−
p+7MnO4−(aq)+q−1I−+xH2O→r+4MnO2(s)+s0I2(s)+yOH−
thus p=2,q=6,r=2,s=3,x=4,y=8