A

Step 1: Understand the initial condition.
Initially, when the body is not submerged in the water, the weights on both sides of the scale are balanced. The weight of the vessel with water equals the weight of the suspended body.

Step 2: Analyze the situation when the body is submerged.
When the body is fully immersed in the water, it experiences an upward buoyant force equal to the weight of the water displaced by the body. According to Archimedes' principle, this buoyant force is present because the body is displacing some volume of water.

Step 3: Determine the forces at play.
As the body is immersed, its effective weight is reduced by the buoyant force. This means the scale pan with the water (which measures the weight of the water along with the buoyant force acting upwards on the submerged body) becomes lighter compared to the suspended body.

Step 4: Restoring equilibrium.
To restore equilibrium, either the amount of water in the vessel needs to be increased (which increases the downward force on the scale with the water) or the weight of the suspended body needs to decrease (which can be done by lowering the mass). Since the system initially balanced in weight, adding water to the vessel compensates for the buoyant force acting on the suspended body, thus restoring the equilibrium.

Conclusion: Increase the amount of water in the vessel to restore equilibrium.