(i) Cyclohexane and n-octane both are non-polar. Hence, they mix completely in all proportions.
(ii) KCl is an ionic compound while n-octane is non-polar. Hence, KCl will not dissolve at all in n-octane.
(iii) CH‌3OH and CH‌3CN both are polar but CH‌3CN is less polar than CH‌3OH. As the solvent is non-polar, CH‌3CN will dissolve more than CH‌3OH in n-octane.
Thus, the order of solubility will be KCl < CH‌3OH < CH‌3CN < Cyclohexane.