Determining hydrocarbon identity from gas density and molar mass

Steps:

• Use ideal gas law to find molar mass: M = (d × R × T) / P, where d = 2.42 g/L, R = 0.0821 L·atm/mol·K, T = 298 K (25°C room temp), P = 1 atm.
• Calculate: M ≈ 2.42 × 0.0821 × 298 / 1 ≈ 59 g/mol.
• Match to gaseous hydrocarbon: C₄H₁₀ (butane) has M = 58 g/mol, fitting closely.
• Skeletal formula for n-butane is a straight chain of four carbons.

Why D is correct:

• D shows the unbranched C₄ chain, matching butane's formula and calculated molar mass via ideal gas law.

Why the others are wrong:

• A: Represents propane (C₃H₈, M=44 g/mol); density would be ~1.8 g/L, too low.
• B: Represents ethane (C₂H₆, M=30 g/mol); density ~1.2 g/L, mismatches.
• C: Represents pentane (C₅H₁₂, M=72 g/mol); density ~2.9 g/L, too high.

Final answer: D