The compound that is a liquid at room temperature and a pressure of 1.00 atmosphere among the given options is C5H12, which is pentane. Pentane (C5H12) has a boiling point of approximately 36-37°C and exists as a liquid under standard room temperature conditions. The other compounds (CH4, C2H6, C3H8, and C4H10) are gases at room temperature and atmospheric pressure.