(a) If good X is measured on the horizontal axis and good Y on the vertical, what can you say about the preferences of someone whose indifference curves are:
i. parallel to the Y axis?
ii. positively sloped with more desirable indifference curves as one moves to the right?
iii. negatively sloped with more desirable indifference curves as one moves to the left?
(b) What is the condition for optimal choice? When will it not hold? Is it a sufficient condition?