In a series circuit with three bulbs, adding another bulb will
a. make the nearest bulb brighter.
b. make some of the bulbs dimmer.
c. make all the bulbs brighter.
d. make all the bulbs dimmer.

Make all the bulbs dimmer.

Explanation:

We know that the voltage across any resistor is given by :

I is the current flowing through the circuit

R is the resistance of the resistor

The brightness of a bulb totally depends on the power delivered to it. It is given in terms of voltage as :

In series circuit of resistors, the same current flows through all the resistors while the voltage divides. When the number of bulbs increases the resistance of circuit also increases. When resistance increases, the power decreases. As result, adding another bulb will make all the bulbs dimmer.

Hence, the correct option is (d).