Materials and Components
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
Resistivity of Ni remains the same
Residual resistivity of Ni at low temperature will increase as Cu atoms act as defect centres
Resistivity of Ni will decrease at all temperatures because Cu is a better conductor than Ni

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Materials and Components
At room temperature the number of conducting electrons in an intrinsic semiconductor

Is almost equal to the number of valence electrons
Is about half the number of valence electrons
Is small as compared to the number of valence electrons
Is a very small fraction of the number of valence electrons

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