Question

In our environment there are so many gases, therefore how can our nose i mean how does it know that we have to take oxygen and not like carbon monoxide or methan

Answer 1

because it may contain any specialised cell

Answer 2

We intake all gases but since persantage of o2 is more in air so it mainly diffuses as you have taken the eg of co if you ar in a place of high concentration of co u feel suffocating because it in your blood forming corbominoxihemoglobin which is bad for human health