Final answer:
The correct answer is (c) a direct relationship between investment and interest rate, while the latter shows no correlation between investment and income.
Step-by-step explanation:
The difference between the investment demand curve and the investment schedule is that the former shows a direct relationship between investment and interest rate, while the latter shows no correlation between investment and income.
The investment demand curve represents how the level of investment changes with varying interest rates. As interest rates decrease, investment increases, and vice versa. On the other hand, the investment schedule shows the level of investment at different levels of income, without considering the interest rate.
Therefore, the correct answer is (c) a direct relationship between investment and interest rate, while the latter shows no correlation between investment and income.