A compound with molecular formula C4H10O3 is converted by the action of acetyl chloride to a compound with molar mass 190. The original compound has:
ROH + CH3COCl ------- ROCOCH3 + HCl
M (M + 42)
Acylation of each OH group results in an increase of molecular mass of 42. In the given problem molecular mass of the compound increases by 84 on acylation. Therefore, the compound has two OH groups.