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

JEE Main · 2025 · 24 Jan 2025 · Shift 2 · Some Basic Concepts of Chemistry

The hydrocarbon

(X)

with molar mass

80 g mol^{- 1}

and

90%

carbon has ____ degree of unsaturation.

Answer: 3

With molar mass

80 g mo l^{- 1}

and 90% carbon, the mass of carbon per mole is

0.90 \times 80 = 72 g

, giving

72/12 = 6

carbon atoms. The remaining mass,

80 - 72 = 8 g

, is hydrogen, giving

8/1 = 8

hydrogen atoms. The hydrocarbon is

C_{6} H_{8}

.

Degree of unsaturation:

DU = \frac{2 C + 2 - H}{2} = \frac{2 ( 6 ) + 2 - 8}{2} = \frac{6}{2} = 3

JEE Main · 2025 · 24 Jan 2025 · Shift 2 · Integer answer