Solution:
The reducing agent that can be used to extract manganese from manganese dioxide is aluminium powder. Manganese is displaced from manganese dioxide by the more reactive aluminium. In other words, when manganese dioxide is heated with aluminium powder, the aluminium powder acts as a strong reducing agent. It will absorb oxygen and become oxidised, resulting in the formation of aluminium oxide and heat.
3MnO2+4Al⟶3Mn+2Al2O3