True/False: When a monopolist is a perfect price discriminator, total surplus can be increased by changing the price (either lowering or raising the price).

Answer:
False. Perfect price discrimination allows a monopolist to produce at the socially efficient level. Therefore, changing the price would only lower total surplus.

True/False: Even in the presence of externalities, we know from the First Welfare Theorem that markets generate Pareto efficient outcomes, or at least outcomes that are close to efficient.

Answer:

False. The First Welfare Theorem assumes there are no externalities. Therefore, the theorem can't be applied when there are externalities. (It could well be true that the market will still generate a Pareto efficient outcome, it's just not guaranteed)

True/False: Under Leontief preferences, there is no substitution effect as prices change.

Answer:
True. Leontief preferences mean that a consumer treats goods as though they were perfect complements (e.g. left shoes and right shoes). Intuitively, changes in price do not cause consumers to substitute left shoes for right shoes. In fact, the only effect is an income effect: real income goes down when prices increase, and real income increases when prices decrease.

True/False: If a game does not have a Nash equilibrium in pure strategies, then it must have a Nash equilibrium in mixed strategies.

Answer:
True. This is because all games have a Nash equilibrium. (By an advanced mathematical concept known as Kakutani's fixed point theorem. However, it's unlikely you need to know this as an undergraduate).