Identify a Hydroxide which is Highly Soluble in Water.

Hint: The ability of a solid, liquid, or gaseous chemical substance called a solute to dissolve in a solid, liquid, or gaseous solvent is known as solubility. The physical and chemical characteristics of the solute and solvent, as well as temperature, pressure, and the presence of additional chemicals (including variations in pH) in the solution, all influence the solubility of a material.

Complete answer:
When a material dissolves, it can either split into ions (an electrolyte) or stay molecular (a non-electrolyte). A strong electrolyte is one that entirely separates into ions, leaving virtually no molecule form behind. A weak electrolyte is one that forms some ions but retains a significant percentage of the molecule form.
When sodium hydroxide (NaOH) dissolves in water, it divides into positively and negatively charged sodium ions (cations) and hydroxide ions (anions). These ions move freely and independently in the water, however anions tend to be more tightly surrounded by cations and vice versa. Although sodium hydroxide is very soluble in water (over 50% by weight), if more than this quantity is added to water at room temperature, a solid will remain at the bottom of the container.
Although the ions are shown as particular forms, they are really surrounded by water molecules. The quantity of water molecules affected by a particular ion is likely to change over time. When sodium hydroxide dissolves, one mole of sodium ions and one mole of hydroxide ions are produced. A 0.5 molal solution of sodium hydroxide is formed when 5 moles of sodium hydroxide are dissolved in 10 kilos of water (sometimes more properly called a 0.5 formal solution). In reality, the solution contains 0.5 molal sodium ions and 0.5 molal hydroxide ions.

Note:
The saturation concentration of a material in a given solvent is the point at which adding more solute does not raise the concentration of the solution and begins to precipitate the excess quantity of solute. The inability to dissolve in a solid, liquid, or gaseous solvent is known as insolubility. The solvent is usually a liquid, which might be a single material or a combination. Solid solution is also a term that can be used, although it is seldom used to refer to a solution in a gas (see vapor–liquid equilibrium instead).