Answer:
The correct answer is: B. The amount of air in a room never changes.
Step-by-step explanation:
- A system is said to be in equilibrium when the net components in the system remains constant (no increase or decrease) with time.
- The air in a room never remains constant and always undergoes dynamic movement into and out of the room. At equilibrium, the net air in the room remains constant as amount of air exiting the room is balanced by the amount of air entering it.
- Evaporation of water in the form of water vapour from a cup into the atmosphere is not in a state of equilibrium as the amount of water evaporating from the cup is not replaced in the cup so there is a net decrease in water level in the cup.
- The decrease in nitrogen percentage in a room is not in equilibrium as the nitrogen concentration of the room is not constant.
- A blade of grass growing taller is not in equilibrium as a constant height of the grasses is not maintained.