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RRB Group D 1 Dec 2025 Shift 2 Solved Paper

Question : 7 of 100

Marks: +1, -0

C_{2}H_{6}

O_{2}

CO_{2}

H_{2}O

Solution:

Concept:

Balancing a chemical equation ensures the number of atoms of each element is equal on both sides, obeying the Law of Conservation of Mass.

Explanation:

Start with the unbalanced equation:

\mathrm{C_2H_6} + \mathrm{O_2} \rightarrow \mathrm{CO_2} + \mathrm{H_2O}

First, balance carbon (C):

\mathrm{C_2H_6}

has 2 C atoms, so place coefficient 2 before

\mathrm{CO_2}

\mathrm{C_2H_6} + \mathrm{O_2} \rightarrow 2\mathrm{CO_2} + \mathrm{H_2O}

Next, balance hydrogen (H):

\mathrm{C_2H_6}

has 6 H atoms, and each

\mathrm{H_2O}

has 2 H atoms, so place coefficient 3 before

\mathrm{H_2O}

\mathrm{C_2H_6} + \mathrm{O_2} \rightarrow 2\mathrm{CO_2} + 3\mathrm{H_2O}

Now, balance oxygen (O): On the right,

2\mathrm{CO_2}

contributes 4 O atoms, and

3\mathrm{H_2O}

contributes 3 O atoms, totaling 7 O atoms.

Thus, on the left, place coefficient

\frac{7}{2}

before

\mathrm{O_2}

\mathrm{C_2H_6} + \frac{7}{2}\mathrm{O_2} \rightarrow 2\mathrm{CO_2} + 3\mathrm{H_2O}

Multiply every coefficient by 2 to clear the fraction:

2\mathrm{C_2H_6} + 7\mathrm{O_2} \rightarrow 4\mathrm{CO_2} + 6\mathrm{H_2O}

The coefficients are 2, 7, 4, and 6 respectively.

This matches option B.

Answer:

2, 7, 4, 6 (Option B)

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