Answer to Question 1
a) Tom is indifferent between consuming at point a or at point b because both points are on the same indifference curve, I1. Tom would prefer to consume at point c rather than point b because point c is on a higher indifference curve, I2 versus I1.
b) Between points a and b, Tom's marginal rate of substitution for a crab is 2 coconuts per crab.
Answer to Question 2
A person has an absolute advantage in the production of a good if he or she is more productive at producing the good. A person has a comparative advantage in the production of a good if he or she can produce it at the lowest opportunity cost.