Why are copper wires used as connecting wires?

Why copper is used to make connecting wires ?

The heating elements of a heater becomes red has but not the connecting wire. Why?

In 15A wiring the copper wire used is thicker as compared to 5A wiring. Is this statement true.

Give reasons for the following: Copper is used in making electric wires.

A 10 meter long wire of uniform cross section of 20 Omega resistance is used as a potentiometer wire. This wire is connected in series with a battery of 5V along with an external resistance of 480 Omega if an unknown emf epsilon is balanced at 600 cm of this wire , calculate the potential gradient of the potentiometer wire.

A 10 meter long wire of uniform cross section of 20 Omega resistance is used as a potentiometer wire. This wire is connected in series with a battery of 5V along with an external resistance of 480 Omega if an unknown emf epsilon is balanced at 600 cm of this wire , calculate the value of the unknown emf.

Which one of the following is best material for making connecting wires?