The correct answer is: A. the marginal utilities of the two goods consumed are equal.
The consumer is said to be in equilibrium, maximizing his total utility, when the marginal utilities of the two goods consumed are equal. This is because the consumer will get the most satisfaction from his consumption when he is getting the same amount of satisfaction from each good. If the marginal utilities of the two goods are not equal, then the consumer can increase his satisfaction by consuming more of the good with the higher marginal utility and less of the good with the lower marginal utility.
Option B is incorrect because the proportions of the marginal utilities and respective prices are not relevant to the consumer’s equilibrium. The consumer only cares about the marginal utilities of the goods, not their prices.
Option C is incorrect because the consumer does not need to get full satisfaction from the consumption to be in equilibrium. He only needs to be getting the most satisfaction possible from his consumption.
Option D is incorrect because the consumer’s feeling of satisfaction with his expenditure on the various goods is not relevant to his equilibrium. The consumer only cares about the marginal utilities of the goods, not his expenditure on them.