Identifying alkanes by general formula CnH2n+2

Steps:

• Recall alkanes are saturated hydrocarbons with single C-C bonds and formula CnH2n+2.
• Examine each molecule: check for only single bonds and matching hydrogen count.
• Count molecules 1, 2, and 4 as alkanes (e.g., CH4, C2H6, C4H10 fit formula).
• Identify molecule 3 as not an alkane (e.g., contains C=C double bond, formula C3H6 ≠ C3H8).

Why C is correct:

• Three molecules match the alkane definition of saturated chains with CnH2n+2, forming the homologous series.

Why the others are wrong:

• A: Underestimates; only one alkane ignores the other two matches.
• B: Still undercounts; misses the third alkane.
• D: Overcounts; includes the unsaturated molecule that breaks the series.

Final answer: C