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Electrical Resistance

The electrical resistance of an electrical conductor is the opposition to the passage of an electric current through that conductor.

SI Unit => Ohm(?)

Supplementary Details: An object of uniform cross section has a resistance proportional to its resistivity and length and inversely proportional to its cross-sectional area. All materials show some resistance, except for superconductors, which have a resistance of zero.A superconductor is active only when its temperature is 0 degree Kelvin. Only then the Resistance becomes 0 ohm.

But the thing is, we haven't been able to achieve 0 degree Kelvin. So the zero Resistance exists theoretically, until today. But there's still superconductors - which has a very negligible resistance, which makes many works easy.

Point of clarification. Superconductors have zero resistance, at temperatures above 0 Degrees Kelvin. So far, the temperatures have to be close to zero degrees Kelvin. The boiling point of Helium is about 4.2 K and it is commonly used for cooling. Many materials that are partial conductors, like niobium, exihibit superconductivity at this sort of temperature.

Good conductors like copper, have lower resistance at low temperature, but don't exhibit superconductivity. It takes a stronger interaction between the electrons and the crystalline lattice for a material to exhibit superconductivity.

Achieving high temperature superconductivity is a technical challenge. The highest critical temperature achieved is mercury barium calcium copper oxide (HgBa2Ca2Cu3O8) at around 133 K. It seems counter intuitive that an oxide, would be a conductor rather than an insulator, but the lattice coupling is crucial.

Liquid nitrogen boils at approximately 77 Kelvin. That temperature is much easier to achieve than 4 Kelvin. So commercial viability lies there.