Question

Name the reducing agent in the following reaction : 3MnO2 +4 Al→3Mn + Al2O3. Which is more reactive Mn or Al and why

Answer 1

reducing agent is the one that itself gets oxidised.
here Mn is getting reduced and while Al is getting oxidised.
so reducing agent is Al
Al is more reactive then Mn bcz of reactivity series order

Answer 2

Al is ‘more reactive’ than Mn as it replaces the Mn from its compound $\mathrm{MnO}_{2}$.

$\bold{3 \mathrm{MnO}_{2}+4 \mathrm{Al} \rightarrow 3 \mathrm{Mn}+\mathrm{Al}_{2} \mathrm{O}_{3}}$

Here $\mathrm{MnO}_{2}$ changes to Mn. The ‘oxidation number’ of Mn in $\mathrm{MnO}_{2}$ is +4 whereas the oxidation number of Mn is zero. Hence the change in oxidation number occurs from +4 to 0. Overall oxidation number decreases hence it is reduction and $\mathrm{MnO}_{2}$ is called as oxidizing agent.

On the contrary, the oxidation number of Al is zero and it changes to +3 in $\bold{\mathrm{Al}_{2} \mathrm{O}_{3}}$. Hence the ‘oxidation number increases’ so it is an oxidation reaction and Al is a reducing agent.