Question

breathing is an involuntary action . why

Answer 1

Breathing is special in several respects: it is the only function you can perform consciously as well as unconsciously, and it can be a completely voluntary act or a completely involuntary act, as it is controlled by two sets of nerves, one belonging to the voluntary nervous system, the other to the involuntary ( ...

Answer 2

Because we cannot control our breathing.
We sometimes didn't know rthat we r breathing but we were and if we try to block our breath then after sometime we will be unconsious but we will breathe.
So it is an involuntary action which is controlled by the Medulla in the hind-brain.