Step-by-step explanation:
In the series combination of the circuit, the amount of the current flowing in the circuit is same but the potential difference in the circuit is different.
The equivalent resistance in the series combination of the circuit is more than the equivalent resistance in the parallel combination.
In the parallel combination of the circuit, the amount of the current flowing in the circuit is different but the potential difference is same.
In the given problem, more light bulbs are added in the series combination of the circuit then the brightness of the bulbs will get decrease. As the total amount of current will get decreased due to the increase in the value of total resistance.