Hi there,

The responsible charge carriers are:

1)solid:

a) conductor- free electrons are the responsibile charge carriers for flow of current.

b) semiconductor- free electrons + holes are the responsibile charge carriers for flow of current.

c) insulator- no charge carriers is responsible for the flow of current as these do not conduct electric current.

2) liquid: positive and negative charged ions are the responsibile charge carriers for flow of current.

3) gas: in ionised gases positive and negative charged ions as well as the free electrons are responsible for the flow of current.

4) vaccum tubes: Free electrons ejected from cathode after heating it are the responsibile charge carriers for flow of current.

Hope it helps!