Indifference curves of imperfect substitutes are concave to the origin' is not the basic property of indifference curves.
Explanation: An indifference curve is a graph showing a combination of two goods that give the consumer equal satisfaction and utility.
The four properties of indifference curves are:
indifference curves can never cross (2) the farther out an indifference curve lies, the higher the utility it indicates, (3) indifference curves always slope downwards, and (4) indifference curves are convex.