Final answer:
When the price of orange juice increases, the demand curve for apple juice will shift to the right due to the substitution effect, meaning that consumers will likely buy more apple juice as a substitute for the now more expensive orange juice.
Step-by-step explanation:
If orange juice and apple juice are substitutes, then when the price of orange juice increases, we would anticipate the demand curve for apple juice to shift to the right, as people will seek out substitutes for the now more expensive orange juice. This is underpinned by the concept of the substitution effect, which is a part of consumer choice theory. The substitution effect states that when a product becomes more costly, consumers will tend to purchase more of its substitutes, assuming the substitutes remain at a lower price. Since orange juice has become more expensive, consumers will likely increase their demand for apple juice, which is a substitute and presumably less expensive now in comparison.
The correct answer to the student's question is 1) The demand curve for apple juice will shift to the right.