(i) Indifference curves have a negative slope. The negative slope of an indifference curve shows that the two goods are substitutes for one another. Therefore, if quantity of one commodity decreases, quantity of the other commodity must increase if the consumer has to stay at the same level of satisfaction.
(ii) Indifference curves are convex to origin. Indifference curves for normal goods are not only negatively sloping, but are also convex to the origin.