According to the image you sent, the correct answer is: b. The net flow of heat energy between the two objects is zero
Two objects are in thermal equilibrium when they are at the same temperature and there is no net flow of heat energy between them.
The other statements are not true:
a. The thermal energies for the two objects are equal
This is not necessarily true. Two objects of different masses can have the same temperature, but different thermal energies.
c. The two objects are at different temperature
This is the opposite of thermal equilibrium.
d. There is a net flow of heat energy from one object to the other
This is only true until the two objects reach thermal equilibrium.
Therefore, the only correct statement is b. The net flow of heat energy between the two objects is zero.