explain how does the resistivity of a conductor depend upon number of density of free electrons and relaxation time

Dear Student,
Resistivity of a conductor is given by the formula,

$\rho$ = m/ne²λ 

where m = mass of  an electron
n = number density of free electron
e = charge on an electron
λ = relaxation time

(1) We can see from the above equation that the resistivity of a conductor is inversely proportional to the number density 'n' of free electrons.So when number density increases then the resistivity decreases .

(2) Again from the given equation the resistivity of a conductor is inversely proportional to the relaxation time λ .So when relaxation time increases then the resistivity also decreases.

Regards