Conductor Resistivity

Answer is C.

If a small amount of Cu is added to Ni conductor, then resistivity of Ni will increase at all temperatures as Cu destroys the periodicity of Ni and acts as defects.

According to Matthiessen rule, electrical resistivity is the sum of two
components: a residual part P_r, and a thermal part P_t

Impurities increases the residual resistivity. Nordheims rule for residual resistivity
helps us the determine the increase in resistivity due to impurities.

Equation for Nordheims rule
is given by:

P_r(x) = A x(1-x)

Where P_r is the residual resistivity,
x is the percentage of impurity

A is the constant that is dependent on impurity and conductor.It depends on the base metal and the impurity. The material factors that influence the constant A includes atomic sizes, crystal structures and electro-negativities.