Which of the following is least likely to dissolve in the polar solvent water?
answer

ethanol
salt
sugar
oil

Like dissolves like and unlike repels like. This applies to the polarity of the solutions. Polar dissolves polar and non-polar does not mix with polar solutions. In this case, the polar substance that can mix with water. Sugar and salt can be dissolved through agitation. Oil which is nonpolar is immiscible in water. Hence answer is D. 

It is a product

Answerδh > 0explanationc₆h₆  (s)  → c₆h₆ (l)if you are changing it from a solid to a liquid, you are pretty much melting the solid. this requires heat energy. therefore, the reaction is endothermic (takes in energy); the system enthalpy increases as the reaction proceeds: δh > 0.