Given the reaction at equilibrium: A (g) + B (g) C (g) + D (g) + heat

As additional A (g) is added to the system at constant temperature, the concentration of B (g)

a

remains the same

b

decrease

c

increases

The concentration of B (g) decrease.

Explanation:

The equilibrium state for a chemical system is characterized by concentrations or partial pressures of reagents and products that remain unchanged over time. Le Chatelier's Principle states that if a system in equilibrium undergoes a change in conditions, it will move to a new position in order to counteract the effect that disturbed it and restore the state of equilibrium.

One of the conditions that can be modified is concentration. When the concentration of one of the substances in an equilibrium system is changed, the equilibrium varies in such a way that it can compensate for this change. When this concentration increases, the system will shift so that it partially uses the added substance. That is, if a reagent is increased, as happens in this casp when A (g) increases, the system will partially consume it, favoring the direct direction of the reaction. In other words, the balance shifts to the right or to the side of the products.

So, the concentration of B (g) decrease.