The correct answer is option (i) weighted index. The textbook explicitly states that 'An index number becomes a weighted index when the relative importance of items is taken care of.' In contrast, a simple aggregative index is described as 'unweighted, because the relative importance of the items has not been properly reflected.' The context explains that in reality, items differ in order of importance—for example, food items occupy a large proportion of expenditure—and a weighted index accounts for these differences in importance among items.