An unsaturated solution is formed when 80 grams of a salt is dissolved in 100 grams of water at 40. this salt could be ?

A simple way to go about this is that we look at the solubility curve, on the x axis we first look at the temperature and then the corresponding value of solute/100g H2O on the y axis, from the 4 curves above only NaNO3 has a curve that can accommodate  80g of salt at 40 without being Saturated since at 40 degrees it can accommodate 105g of salt to become completely Saturated.

Answer is to avoid experimental error

Noble gases is far right