Micro-economics, Properties of Indifference Curve(1)Downward sloping to the right:(a)Indifference curve cant be horizontal straight line.

Indifference curve cannot be horizontal straight line:
Instead of sloping downward to the right if an indifference curve is a horizontal straight line, the consumer will remain on the same indifference curve and at the same level of satisfaction even though he has more units of mangoes and same amount of apples. The addition of mangoes without losing any of apples must take him onto the higher indifference curve rather than keeping him on old indifference curve hence indifference curve cannot be a horizontal straight line.