JEE Main 2025 Jan 24 Shift 2, Chemistry Q24: Aromatic Hydrocarbons: Benzene

JEE Main2025Jan 24, Shift 2Chemistry

The hydrocarbon (X) with molar mass 80 g mol $^{- 1}$ and 90% carbon has ________ degree of unsaturation.

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Solution

Mass of carbon per mole of $X$ : $\frac{90}{100} \times 80 = 72 g \Rightarrow n_{C} = \frac{72}{12} = 6$ .

Remaining mass is hydrogen: $80 - 72 = 8 g \Rightarrow n_{H} = \frac{8}{1} = 8$ .

Molecular formula: $C_{6} H_{8}$ .

Degree of unsaturation $= \frac{2 C + 2 - H}{2} = \frac{2 ( 6 ) + 2 - 8}{2} = \frac{6}{2} = 3$ .

Answer: 3

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