When a box of chocolate bars is in mechanical equilibrium, what can be correctly said about all the forces that act on it?

All the forces are opposite and equal and will give net force zero.

Explanation:

Mechanical equilibrium is the equilibrium in which the total force on the system is zero means the system is neither accelerated nor any kind of torque on the system.

The mechanical system can also be defined as the equal forces are applied in opposite direction in a system which cancels out all the forces, will give net force zero.

Therefore, when a box of chocolate bars is in mechanical equilibrium all the forces in this system are equal and the opposite which balances each other will give net force zero.