In standard-state conventions for gases, what is the reference pressure?

• A. 1 bar
• B. 0.987 atm
• C. 1 atm
• D. 2 atm

Answer: (C)

The reference pressure in standard-state conventions for gases is the pressure at which standard thermodynamic properties are defined. In many chemistry contexts and exams, that reference pressure is taken as 1 atmosphere. That’s why 1 atm is the best answer here. It’s worth noting that modern IUPAC standards often use 1 bar as the reference pressure, and 1 bar is about 0.987 atm while 1 atm is about 1.013 bar, but the convention used in this question aligns with 1 atm.