Correct Answer: The assertion is correct, but the reason is incorrect.

Solution : The correct answer is (C) The assertion is correct, but the reason is incorrect.

The assertion that expansion in demand leads to an upward movement along the same demand curve is correct. When demand for a commodity increases, it leads to a higher quantity demanded at each price level. This results in an upward shift along the demand curve.

However, the reason provided, which states that an upward movement along the same demand curve occurs due to an increase in the price of the given commodity, is incorrect. Changes in the price of a commodity lead to movements along the demand curve, not shifts. When the price of a commodity increases, it leads to a decrease in quantity demanded, resulting in a movement upwards along the existing demand curve. Conversely, a decrease in the price of a commodity leads to an increase in quantity demanded, resulting in a movement downwards along the demand curve.

In summary, the assertion is correct, but the reason provided to support it is incorrect.