When calculating the equilibrium constant, aqueous solutes must be expressed in moles per liter (m), and gases must be expressed in pressure as bars. this is . there are no other ways to express pressure or concentration other than bars or moles per liter (m). b. they are dimensionless ratios of the actual concentration or pressure divided by standard state concentration, which is 1 m for solutions and 1 bar for gases. c. these are the only units of concentration and pressure that are independent of temperature. d. the dimensionless ratios are always unity (1) because the concentration of the solute or pressure of the gas are divided by standard state concentrations.

B. They are dimensionless ratios of the actual concentration or pressure divided by standard state concentration, which is 1 M for solutions and 1 bar for gases.

Explanation:

Activity of a substance is defined as the ratio of an effective concentration or an effective pressure to a standard state pressure or a standard state pressure. It is usually a unit less ratio.

Concentrations in an equilibrium constant are really dimensionless ratios of actual concentrations divided by standard state concentrations. Since standard states are 1 M for solutes, 1 bar for gases, and pure substances for solids and liquids, these are the units to be used.

Hence, activity is a fudge factor to ideal solutions that correct the true concentration. Activity of a gas and solute concentration is a ratio with no unit.