The correct answer is: A. Slope of MC and Mr is the same.
Profit is maximum when marginal revenue (MR) equals marginal cost (MC). This is because when MR equals MC, the firm is producing the quantity of output where the additional revenue from selling one more unit of output is equal to the additional cost of producing one more unit of output. In other words, the firm is producing at the point where the marginal benefit of producing one more unit of output is equal to the marginal cost of producing one more unit of output.
The slope of the MC curve is the marginal cost of producing one more unit of output. The slope of the MR curve is the marginal revenue from selling one more unit of output. When the MC curve and the MR curve intersect, the slope of the MC curve is equal to the slope of the MR curve. This is the point where profit is maximized.
Option B is incorrect because the slope of the TC curve is not equal to the slope of the TR curve. The slope of the TC curve is the marginal cost of producing one more unit of output. The slope of the TR curve is the marginal revenue from selling one more unit of output. The two curves do not intersect, so there is no point where the slope of the TC curve is equal to the slope of the TR curve.
Option C is incorrect because the slope of the AC curve is not equal to the slope of the AR curve. The slope of the AC curve is the average cost of producing one more unit of output. The slope of the AR curve is the average revenue from selling one more unit of output. The two curves do not intersect, so there is no point where the slope of the AC curve is equal to the slope of the AR curve.
Option D is incorrect because the slope of the MC curve is equal to the slope of the MR curve at the point where profit is maximized.