Step 1: Understand the concept of hydration.
In aqueous solution, when cations like and dissolve, they attract water molecules around them. This is called hydration. The number of water molecules surrounding the ion is determined by the size of the ion and its charge density. Smaller ions with higher charge densities can attract more water molecules.
Step 2: Hydration of ion.
The ion, also known as a proton, is extremely small with a high charge density. Because of this, it is surrounded by a small number of water molecules, typically around 4. These water molecules surround the ion in a tetrahedral arrangement.
Step 3: Hydration of ion.
The ion is also small but slightly larger than . It also has a high charge density, but due to its larger size compared to , it is surrounded by a greater number of water molecules, usually around 6. These water molecules arrange themselves around the ion in a more symmetrical octahedral structure.
Step 4: Conclusion.
Thus, the number of water molecules surrounding is 4 and the number surrounding is 6, which corresponds to option (B).