Thermal equilibrium is reached electrical forces are balanced the sound vibrations reach a high pitch two objects in contact with each other are the same temperature objects have enough kinetic energy for them be at terminal velocity the net force on an object is zero

Option (c) is the correct answer.

Explanation:

When there is no exchange of heat between two substances which are physically connected to each other then it is said that thermal equilibrium has reached.

Also at thermal equilibrium the temperature for two objects or substance becomes same.  

Thus, we can conclude that out of the given options thermal equilibrium is reached when two objects in contact with each other are the same temperature.

answer: option c. i.e. electric current flowing “downhill” from the negative electrode to the positive electrode in a battery

explanation:

the water analogy to the circuits define the pipes (water flows) to the electric current. now, we know that the electric current flows from the positive terminal to the circuit (as shown in the diagram attached).

hence, option c is the correct answer.