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Question

In the following redox reaction, which compound is acting as a reducing agent ?
\(N_2H_4 + 2H_2O_2 \rightarrow N_2 + 4H_2O\)

This question was previously asked in
NDA 2 2025 GAT Question Paper (14-Sep-2025)
The correct answer is
\(N_2H_4\)

Redox Reaction Analysis: Identifying the Reducing Agent

This question asks us to identify the reducing agent in the given redox reaction: \(N_2H_4 + 2H_2O_2 \rightarrow N_2 + 4H_2O\)

Understanding Redox Reactions and Agents

In a redox reaction, electrons are transferred between chemical species. This involves changes in oxidation states.

  • Oxidation is the loss of electrons or an increase in oxidation state.
  • Reduction is the gain of electrons or a decrease in oxidation state.
  • A reducing agent is a substance that causes reduction in another substance and is itself oxidized.
  • An oxidizing agent is a substance that causes oxidation in another substance and is itself reduced.

To find the reducing agent, we need to determine the oxidation states of the elements in the reactants and see which substance gets oxidized (its oxidation state increases).

Calculating Oxidation States

Let's calculate the oxidation states for each element in the reactants and products:

Reactants:

1. \(N_2H_4\) (Hydrazine)

  • Hydrogen (H) typically has an oxidation state of +1.
  • Let the oxidation state of Nitrogen (N) be \(x\).
  • The sum of oxidation states in a neutral molecule is 0.
  • Equation: \(2x + 4(+1) = 0\)
  • \(2x + 4 = 0\)
  • \(2x = -4\)
  • \(x = -2\). The oxidation state of N in \(N_2H_4\) is -2.

2. \(H_2O_2\) (Hydrogen Peroxide)

  • Hydrogen (H) has an oxidation state of +1.
  • Let the oxidation state of Oxygen (O) be \(y\).
  • Equation: \(2(+1) + 2y = 0\)
  • \(2 + 2y = 0\)
  • \(2y = -2\)
  • \(y = -1\). The oxidation state of O in \(H_2O_2\) is -1.

Products:

1. \(N_2\) (Nitrogen Gas)

  • Nitrogen is in its elemental form.
  • The oxidation state of an element in its elemental form is 0.
  • The oxidation state of N in \(N_2\) is 0.

2. \(H_2O\) (Water)

  • Hydrogen (H) has an oxidation state of +1.
  • Let the oxidation state of Oxygen (O) be \(z\).
  • Equation: \(2(+1) + z = 0\)
  • \(2 + z = 0\)
  • \(z = -2\). The oxidation state of O in \(H_2O\) is -2.

Analyzing Oxidation State Changes

Now, let's compare the oxidation states from reactants to products:

  • Nitrogen (N): Changes from -2 in \(N_2H_4\) to 0 in \(N_2\). The oxidation state increases, meaning Nitrogen is oxidized.
  • Oxygen (O): Changes from -1 in \(H_2O_2\) to -2 in \(H_2O\). The oxidation state decreases, meaning Oxygen is reduced.
  • Hydrogen (H): Remains at +1 in all species (\(N_2H_4\), \(H_2O_2\), \(H_2O\)).

Determining the Reducing Agent

Since \(N_2H_4\) is the substance that gets oxidized (its Nitrogen atom's oxidation state increases from -2 to 0), it acts as the reducing agent. It causes the reduction of \(H_2O_2\) (where Oxygen's oxidation state decreases from -1 to -2).

Compound Element Initial Oxidation State Final Oxidation State Change Role
\(N_2H_4\) N -2 0 (in \(N_2\)) Increase (+2) Reducing Agent
\(H_2O_2\) O -1 -2 (in \(H_2O\)) Decrease (-1) Oxidizing Agent

Therefore, \(N_2H_4\) is the reducing agent in this reaction.

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Similar Questions

  1. Which of the following are oxidation reactions?
    I. Rusting of iron
    II. Burning of fuel
    III. Rancidity of oils and fats
    IV. Browning of fruits
    Select the correct answer using the code given below.
  2. Consider the following pairs of reactions and properties :
    ReactionsProperties
    I. \(\text{Fe} \, (s) + 2\text{HCl} \, (aq) \rightarrow \text{FeCl}_2 \, (aq) + \text{H}_2 \, (g)\)\(\text{Fe}\) is reductant
    II. \(\text{Zn} \, (s) + \text{CuSO}_4 \, (aq) \rightarrow \text{ZnSO}_4 \, (aq) + \text{Cu} \, (s)\)\(\text{Cu}\) is being reduced
    III. \(\text{Br}_2 \, (l) + 2\text{I}^- \, (aq) \rightarrow 2\text{Br}^- \, (aq) + \text{I}_2 \, (s)\)\(\text{Br}_2\) is reductant
    IV. \(\text{CH}_4 \, (g) + 2\text{O}_2 \, (g) \rightarrow \text{CO}_2 \, (g) + 2\text{H}_2\text{O} \, (l)\)\(\text{C}\) atom in \(\text{CH}_4\) is oxidized

    Which of the above pairs are correct?

Important Questions from Redox Reactions

  1. Nitric acid is reduced to nitrogen dioxide in which of the following reactions?

  2. The role of H3PO4 in the estimation of Fe(II) with K2Cr2O7 using diphenylamine sulphonate as indicator is to

  3. In reaction, 2Na2S2O3 + I2 → A + 2NaI; A will be _________.

  4. Number of electrons (x) involved in the following reaction is :
    \(N \equiv N+ 8H^{+}+x \rightarrow 2N H^{3}+ H_{2}\)

  5. The differences between crude birth rate and crude death rate in a population is called
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