Answer:
B. begin with a hypothesis
Explanation:
As we have the balanced reaction equation is:
N2O4 (g) ↔ 2NO2(g)
from this balanced equation, we can get the equilibrium constant expression
KC = [NO2]^2[N2O4]^1
from this expression, we can see that [NO2 ] is with 2 exponent of the stoichiometric and we can see that from the balanced equation as NO2
is 2NO2 in the balanced equation.
and [N2O4] is with 1 exponent of the stoichiometric and we can see that from the balanced equation as N2O4 is 1 N2O4 in the balanced equation.
∴ the correct exponent for N2O4 in the equilibrium constant expression is 1
Answer : At constant pressure work is done by the system on the surroundings.
Explanation :
Work done : Any quantity that flows across the boundary of a system during a change in its state and it completely convertible into the lifting of a weight in the surroundings.
Formula for work done is:

Sign convention :
- When volume expand then system work that means work done by the system.
w = (-ve)
- When volume compress then surrounding work that means work done on the system.
w = (+ve)
The given reaction is:

This is a evaporation process in which phase changes from liquid state to gaseous state at constant temperature.
At constant pressure, work depends only on volume.
In evaporation process, the volume expand that means work is done by the system on the surroundings.
Sign convention is, w = (-ve)
Thus, at constant pressure work is done by the system on the surroundings.