Final answer:
The quantity demanded (Qd) increases when the price of popcorn decreases from $5 to $3 a bag.
Step-by-step explanation:
When the price of popcorn decreases from $5 to $3 a bag, the quantity demanded (Qd) increases. This is because consumers are more willing to buy more popcorn at the lower price. The demand (D) for popcorn remains the same as it refers to the overall desire for popcorn at different price levels.