1. When the demand line is perfectly elastic, there is no deadweight loss after taxation.
2. Firms must not operate if the market price is less than ‘break-even' price.
3. Price floor would lead to surplus in the market.
4. When the supply line is perfectly inelastic, there is no deadweight loss after subsidy.
5. A positive externality for individual X can not be a negative externality for individual Y.