Answer: -
Solubility of a substance depend on the balance of intermolecular forces between the solvent and solute, and the entropy change that accompanies this process.
Temperature and pressure also plays a role in solubility.
A solution having Group 1 cations like lithium, sodium, potassium etc are always soluble.
A solution having NH₄⁺ is soluble.
All salts with anion as nitrates, acetates, chlorates, and perchlorates are soluble in water.
Principal shell shows the main energy level, in that there are some more energy levels. This is how the atomic structure is defined according to the Quantum Mechanical model of atom. So exactly why do subshells exist and all i don't know