* Polarity: Sodium chloride is a highly polar ionic compound. The strong electrostatic attraction between the positively charged sodium ions (Na+) and the negatively charged chloride ions (Cl-) makes it very difficult to break apart in a non-polar solvent.
* Diethyl Ether: Diethyl ether (CH3CH2OCH2CH3) is a non-polar solvent. It has a low dielectric constant, meaning it cannot effectively separate and solvate the charged ions of sodium chloride.
In short: "Like dissolves like". Polar solvents dissolve polar solutes, and non-polar solvents dissolve non-polar solutes. Since sodium chloride is polar and diethyl ether is non-polar, they are not compatible for dissolution.
