Answer: The volume of the balloon up there is 6.192 L.
Explanation:
Given:
= 1.80 L,
= 785 mm Hg (mm Hg = 0.00131579) = 1.032 atm
= 0.300 atm,
= ?
Formula used to calculate volume is as follows.

Substitute the value into above formula as follows.

Thus, we can conclude that the volume of the balloon up there is 6.192 L.
I am sure, the answer is variant B.
Answer:
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.