How the revelation of the fact that junk-foods might be injurious to health can affect the Demand Curve of junk-foods.

Option 1 -> Upward shift is not standard terminology for demand curve shifts.

Option 2 -> Downward shift is not standard terminology for demand curve shifts.

Option 3 -> Rightward shift means increase in demand, which contradicts the negative health revelation.

Option 4 -> Leftward shift means decrease in demand at all price levels.

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Hence, Option 4: Leftward shift in demand curve of junk-foods -> When consumers learn that junk food is injurious to health, their preferences change negatively. This is a non-price determinant of demand. At every price level, consumers will now demand less quantity of junk food than before. This causes the entire demand curve to shift to the left (or decrease). A leftward shift represents a decrease in demand, meaning lower quantity demanded at each price point due to changed consumer preferences and health concerns. -> correct