Question

what may happen if the filament of one of the bulbs in your first setup melts why​

Answer 1

Answer:

if the filament melts the circuit will break and there will be no current flowing in the circuit.

Answer 2

The observation and reason is as follows -

1. On melting of filament in the bulb, the circuit will break and hence will not be able to conduct electricity. Thus, the rest connected bulbs will not glow.
2. Filament of bulbs are made of an alloy having high melting point, so that it remains undamaged on increase in temperature.
3. Commonly used filament in bulbs is made of tungesten.