The correct answer is option 'B' - blue.

When copper sulfate crystals are dissolved in water, they dissociate into copper ions (Cu2+) and sulfate ions (SO4^2-). These ions are then surrounded by water molecules and form a hydrated copper sulfate solution.

Here is a detailed explanation:

1. Dissociation of Copper Sulfate:
- When copper sulfate crystals (CuSO4) are added to water, they dissociate or break apart into their constituent ions.
- The chemical equation for this dissociation is:
CuSO4(s) → Cu2+(aq) + SO4^2-(aq)

2. Formation of Hydrated Copper Sulfate:
- The copper ions (Cu2+) and sulfate ions (SO4^2-) are surrounded by water molecules due to their polarity.
- The water molecules form bonds with the copper and sulfate ions through electrostatic attractions, resulting in the formation of a hydrated copper sulfate solution.
- The resulting compound is called hydrated copper sulfate because it contains water molecules.

3. Color of the Solution:
- The blue color of the solution is due to the presence of the hydrated copper ions (Cu2+).
- Copper ions absorb light in the red-orange region of the electromagnetic spectrum and reflect or transmit blue light.
- This selective absorption of light gives the solution its characteristic blue color.

4. Explanation of Other Options:
- Option 'A' - brown: Copper sulfate does not produce a brown solution when dissolved in water. Brown coloration may be due to the presence of impurities or oxidation of copper.
- Option 'C' - green: Copper sulfate in water does not result in a green solution. Green coloration may be due to the presence of other compounds or impurities.
- Option 'D' - red: Copper sulfate does not produce a red solution when dissolved in water. Red coloration may be due to the presence of other substances or impurities.

In conclusion, when copper sulfate crystals are dissolved in water, the resulting solution is blue in color due to the presence of hydrated copper ions.

Blue
because solution of copper sulphate is blue vitriol