Which of the following statements is correct?

Analyze the question: We must test each statement about alkanes and decide which one is true.

Concept: Alkanes are saturated hydrocarbons with the general formula CₙH₂ₙ₊₂. They react with halogens by substitution (not addition), and their boiling points increase as chain length increases.

Checking each option:

• A. Addition reactions occur between alkanes and chlorine. False. Alkanes are saturated, so they undergo substitution with chlorine in the presence of UV light. Addition reactions are typical of alkenes and alkynes.

• B. Butane has a lower boiling point than propane. False. Butane (C₄H₁₀, about 0 °C) has a higher boiling point than propane (C₃H₈, about -42 °C), because the larger molecule has stronger van der Waals forces.

• C. Pentane has five isomers. False. Pentane (C₅H₁₂) has three isomers: n-pentane, 2-methylbutane (isopentane) and 2,2-dimethylpropane (neopentane).

• D. An alkane with 49 carbon atoms contains 100 hydrogen atoms. Using CₙH₂ₙ₊₂ with n = 49: H = 2(49) + 2 = 98 + 2 = 100 True.

Tip: For alkane questions, remember "2n + 2" for hydrogens. Also remember that alkanes substitute and alkenes add. For boiling points, a bigger molecule means a higher boiling point, and more branching lowers it.