Zeroth law of thermodynamics is related to:
(A) temperature
(B) heat
(C) chemical equilibrium
(D) internal energy

Hint: We should know that the zeroth law of the thermodynamics states that if two thermodynamic systems are in thermal equilibrium and if they are placed with a third system, then the whole system or all the three systems is said to be in thermal equilibrium.

Complete step by step solution:
To know the answer, first of all, let us know about what is zeroth law.
The zeroth law of thermodynamics was introduced by Ralph. H. Fowler and it is one of the four basic laws of thermodynamics. The law frames the concept of temperature, which can be used to measure the thermal equilibrium between systems.
Consider three thermodynamic systems A, B and C. So, when a body ‘A’ is in thermal equilibrium with another body ‘B’, and is also separately in thermal equilibrium with the system ‘C’, then the systems ‘B’ and ‘C’ are said to be in the thermal equilibrium with each other. This statement forms the definition of the zeroth law of thermodynamics. In other words, “systems that are in thermal equilibrium or chemical equilibrium will exist at the same temperature”.
Even if there is no direct contact between the two thermodynamic systems, it can still transfer heat between each other by means of radiation of heat. But, according to the zeroth law of thermodynamics, if the systems are in thermal equilibrium, no heat flow will take place.
So, we can see that the zeroth law of thermodynamics takes into account that temperature is something worth measuring and it decides whether the systems are in chemical equilibrium.

Hence, the correct option will be both (A) and (C).

Note: Two bodies are said to be in thermal or chemical equilibrium when two bodies at different temperatures are brought into, and after some time they acquire a common temperature. The most common application of the zeroth law is seen in thermometers.