Question

How does the presence of impurities in a metal affect its resistance ?

Answer 1

Excess the impurities higher would be the resistance and vice versa.

Answer 2

The resistance of a metal is highly affected by "presence of impurities" in a metal.

$\bold{\mathrm{R \propto I}}$

Where,

R be the resistance of the metal  

I be the amount of impurities present in the metal

The above relation shows that resistance of a metal is directly proportional to the presence of impurities in the metal i.e., the more the impurity the more will be the resistance of the metal.

Pictures (a), (b), and (c) represent metal states of increasing level of impurities

The order of resistance be: (c) > (b) > (a)