Materials and Components
The elements which become superconducting at extremely low temperatures are

Good conductors at room temperature
Relatively poor conductors at room temperature
Insulators at room temperature
Ferromagnetic at room temperature

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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
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
Resistivity of Ni remains the same

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Materials and Components
Electrical contact materials used in switches, brushes, relay must possess

Low thermal conductivity and high melting point
High thermal conductivity and high melting point
Low thermal conductivity and low melting pointL
High thermal conductivity and low melting point

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