Final answer:
The largest impact of a price floor occurs when it is set substantially above the equilibrium price, causing a surplus, while a price ceiling has the largest effect when it is set substantially below the equilibrium price, causing a shortage.
Step-by-step explanation:
The most accurate statement concerning the impact of a price floor is that it will have the largest effect if set substantially above the equilibrium price. When a price floor is placed significantly above the market-clearing level, it causes a surplus because the price is higher than what many consumers are willing to pay, and suppliers are producing more than what is being consumed at that price. On a demand and supply diagram, this is represented by a horizontal line above the equilibrium point where supply exceeds demand.
In contrast, a price floor set slightly above, at, or below the equilibrium price would have a lesser, or no impact. A price floor below equilibrium is non-binding and thus will not affect the market. The case is similar for a price floor exactly at the equilibrium since the market naturally settles at this price. A floor slightly above might cause a marginal surplus but is close to the balance of supply and demand.
Regarding a price ceiling, the largest effect occurs when it is set substantially below the equilibrium price. This results in a shortage as the ceiling makes the market price artificially low, causing demand to exceed what suppliers are willing or able to produce at that price level. This is shown on the diagram as a horizontal line below the equilibrium where demand outstrips supply.