Concept:Impurities affect the melting point by making it melt over a wider temperature range.Explanation:A pure substance has a sharp, definite melting point.An impure substance melts gradually over a range of temperatures.A wide melting point range therefore shows that the substance is impure.Difficulty in dissolving, low melting point, or colour are not reliable indicators of impurity.Answer:A. its melting point range is wide