Q.

Manganese dioxide (MnO₂) reacts with hydrochloric acid (HCl) to produce magnesium chloride (MgCl₂), water (H₂O), and chlorine (Cl₂) gas. The chemical equation involved in the reaction is given as:

MnO₂ + 4 HCl → MnCl₂ + 2 H₂O + Cl₂

Which of the following substances is reduced in the given reaction?

Moderate

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HCl

H₂O

MnO₂

MnCl₂

answer is C.

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Detailed Solution

Understanding Redox Reactions

Oxidation: A substance loses electrons, gains oxygen, or loses hydrogen.
Reduction: A substance gains electrons, loses oxygen, or gains hydrogen.

Step-by-Step Analysis of the Reaction

Reactants and Products:
- MnO₂: Manganese dioxide.
- HCl: Hydrochloric acid.
- Products: MnCl₂, H₂O, and Cl₂.
Role of MnO₂:
- MnO₂ starts as manganese dioxide, which contains manganese in a +4 oxidation state.
- In MnCl₂, manganese transitions to a +2 oxidation state.
- The reduction of MnO₂ occurs because it loses oxygen during the reaction, thereby gaining electrons.
Reduction Process:
The loss of oxygen from MnO₂ results in the formation of MnCl₂. This loss of oxygen qualifies MnO₂ as the reduced substance in this redox reaction.
Oxidation Process (for comparison):
HCl is oxidized as chlorine in Cl₂ changes from -1 to 0 oxidation state.