A chamber contains monoatomic 'He' at STP, determine its number density

Answer

`2.68 xx 10^(25) m^(-3)`

Explanation

Number density `= (P)/(kT)` (where, k = Boltzmann constant)
`PV = nRT`
`= (n xx N) (R)/(N) T`
`= (n xx N) kT`
`(P)/(kT) = (n xx N)/(V)` = number density
`:.` Number density `= (1.01 xx 10^(5))/(1.38 xx 10^(-23) xx 273) = 2.68 xx 10^(25) m^(-3)`