Balance Reading with Water Only
When the beaker containing water is placed on the platform of the spring balance, the balance reads 1.5 kg. This reading is the weight of the water present in the beaker.

Mass and Density of the Stone
The stone has a mass of 0.5 kg and a density of 500 kg/m3. The mass of the stone represents the total amount of matter present in it, while the density indicates how tightly the matter is packed within the stone.

Immersion of the Stone in Water
When the stone is immersed in water without touching the walls of the beaker, it displaces a certain volume of water. This displacement occurs because the stone takes up space within the beaker, causing the water level to rise.

Archimedes' Principle
According to Archimedes' principle, the buoyant force experienced by an object submerged in a fluid is equal to the weight of the fluid displaced by the object. This principle explains why objects appear to weigh less when submerged in a fluid.

Balance Reading after Immersion
When the stone is immersed in water, it displaces a certain volume of water. This displaced water has a weight equal to the weight of the stone. As a result, the balance reading will decrease by the weight of the stone (0.5 kg) when the stone is immersed in water.

Therefore, the balance reading will now be 1.5 kg - 0.5 kg = 1 kg.

Explanation in Summary
- The initial balance reading of 1.5 kg represents the weight of the water in the beaker.
- When the stone is immersed in water, it displaces a certain volume of water.
- The displaced water has a weight equal to the weight of the stone.
- According to Archimedes' principle, the buoyant force equals the weight of the displaced water.
- The balance reading decreases by the weight of the stone when it is immersed in water.
- Thus, the balance reading becomes 1 kg after immersion.

By following these steps, you can determine the change in the balance reading when a stone of known mass and density is immersed in water without touching the walls of a beaker.

1.75