How do impurities and temperature affect electrical resistivity of metals?

Ans:

Temperature effect on resistivity:

Any increase in temperature of a conductor increases thermal agitation of metallic ions as they vibrate about their mean positions. This reduces the mean free path and restricts the flow of  electrons,  hence reducing  the  conductivity  of  material  and  increasing  its resistivity.

Ρt = Ρω [1+ α0 (t− 20)]
Ρt → resistivity at temperature
Ρ20 → resistivity at 200c.
α0 → Coefficient of temperature
Which is positive.