Saturated hydrocarbons have only single C-C bonds

Steps:

• Identify saturated hydrocarbons as those with carbon and hydrogen atoms connected solely by single bonds, no double or triple bonds.
• Examine structure 1: all C-C bonds are single → saturated.
• Examine structure 2: all C-C bonds are single → saturated.
• Examine structure 3: contains a C=C double bond → unsaturated.
• Examine structure 4: all C-C bonds are single → saturated.

Why A is correct:

• Option A correctly identifies structures 1, 2, and 4 as having only single C-C bonds, matching the definition of saturated hydrocarbons (general formula CₙH₂ₙ₊₂ for alkanes).

Why the others are wrong:

• B includes structure 3, which has a double bond and is unsaturated.
• C excludes structure 1, which is saturated, and includes unsaturated structure 3.
• D excludes structure 2, which is saturated, and includes unsaturated structure 3.

Final answer: A