Explanation:

In a redox (reduction-oxidation) reaction, there are two species involved: the species that undergoes oxidation and the species that undergoes reduction. The species that undergoes reduction is called the reducing agent.

Redox Reactions:

Redox reactions involve the transfer of electrons between species. One species loses electrons (undergoes oxidation) and another species gains those electrons (undergoes reduction). This transfer of electrons allows for the balancing of charges and leads to the formation of new compounds.

Reducing Agent:

The reducing agent is the species that donates electrons and undergoes oxidation. It is responsible for causing the reduction of another species by providing electrons. The reducing agent itself gets oxidized in the process.

Example:

Let's take the reaction between potassium permanganate (KMnO4) and hydrogen peroxide (H2O2) as an example:
2KMnO4 + 3H2O2 → 2MnO2 + 2KOH + 3O2 + 2H2O

In this reaction, the Mn in KMnO4 undergoes a reduction from a +7 oxidation state to a +4 oxidation state, while the H2O2 gets oxidized to form water. In this case, H2O2 acts as the reducing agent because it donates electrons to MnO4. The MnO4 is the species that undergoes reduction.

Importance of Reducing Agent:

The reducing agent plays a crucial role in redox reactions as it provides the electrons necessary for the reduction of another species. Without a reducing agent, the reduction process would not occur, and the overall reaction would not be balanced.

Therefore, the correct answer is option B) Reducing agent.