Indifference curves are normally convex to the origin because of the principle of:

1. As more X is substituted for Y, the consumer gives up less and less Y for each extra X. 2. This diminishing marginal rate of substitution produces the convex shape. 3. Constant MRS gives a straight line and increasing MRS gives concavity, while MU of money is unrelated, so those options are wrong. _Source: ICAI BoS CA Foundation Paper 4 Business Economics, Ch 2 Unit II "Theory of Consumer Behaviour", p.16_