If a sample of oxygen gas is collected over water at a pressure of 0.921 atm and 23 °C, what is the partial pressure of oxygen alone? (Vapor pressure of water at 23 °C is 21.1 mmHg)
A) 0.900 atm
B) 0.921 atm
C) 0.921 + 21.1 mmHg
D) 0.921 - 21.1 mmHg