Three Birds each having power B …

Here we are basically analyzing Series and Parallel Circuits.
Let us first understand some characteristics.
★ Series Circuit
→ Current through each resistor is same.
→ Voltage Drop is different across each resistor.
★ Parallel Circuit
→ Current is different through each resistor.
→ Voltage Drop is the same across each resistor.
Coming to the question: Three bulbs are connected, once in a Series Circuit, and once in a Parallel Circuit.
Let us assume that the battery is of Voltage V.
(i) In Series Circuit, the voltage drops across the bulbs. Each bulb has a voltage drop of (V/3) across it.
Each bulb glows with the same brightness.
In Parallel Circuit, each bulb receives a Voltage V.
Again, each bulb glows with the same brightness.
However, the bulbs in Parallel Circuit glow with more brightness as compared to bulbs in Series Circuit.
The reason is simply that Parallel Circuit Bulbs receive more Voltage.
(ii) One bulb is fused.
In Series Circuit, if one bulb is fused, all other bulbs will stop working. Because the current cannot flow to the other bulbs
However, in Parallel Circuit, there are still other pathways for current to flow.
The fused bulb will stop working, but the other bulbs will continue to glow with the same brightness.
(iii) The diagram is attached.