Which of the following shows the structural formula for pentane?

• A. CH3-CH2-CH2-CH2-CH3
• B. CH4
• C. CH3-CH3
• D. CH3-CH2-CH2-CH3

Answer: (A)

To show pentane’s structure, you need a continuous chain of five carbon atoms with hydrogens filling the remaining valences: ends are CH3 groups and the carbons in the middle are CH2 groups, giving CH3-CH2-CH2-CH2-CH3. This explicitly contains five carbons, matching pentane’s formula C5H12. The other options represent fewer carbons: CH4 is methane (1 C), CH3-CH3 is ethane (2 C), and CH3-CH2-CH2-CH3 is butane (4 C). Therefore, the structure with five carbons in a row is the correct representation for pentane.