Final answer:
Without assuming standard temperature and pressure conditions or any additional information such as pressure, we cannot accurately determine the moles of gas from the provided volume of 890.0 ml at 21.0 degrees Celsius.
Step-by-step explanation:
The student is asking how many moles of gas are contained in 890.0 ml at 21.0 degrees Celsius. The molar volume of 22.4 L applies to gas at standard temperature and pressure (STP), which is a temperature of 0°C and a pressure of 1 atm. To find the moles at 21°C, we would typically need to use the ideal gas law, but since there's no pressure given or indication to assume STP, we cannot accurately determine the moles of gas.
Assuming we could treat the condition as STP, or had pressure information to use the ideal gas law, we would calculate the moles of gas by dividing the volume of the gas by the molar volume of 22.4 L, which is the volume that one mole of an ideal gas occupies at STP. Please confirm if any additional information, such as pressure or if we should assume STP conditions, is available.