The internal energy of a system depends on what?

Assertion $(A)$: The zeroth law of thermodynamics leads to the concept of temperature.
Reason $(R)$: The zeroth law states that two systems in thermal equilibrium with a third system are in thermal equilibrium with each other.
The correct option among the following is:

State the sign convention for heat and work in thermodynamics.

The energy supply being cut off,an electric heater element cools down to the temperature of its surroundings,but it will not cool further because:

What are state variables?

State the Zeroth Law of Thermodynamics.