Arrange the following in decreasing order of number of molecules contained in:
(A) 16 g of \( O_2 \)
(B) 16 g of \( CO_2 \)
(C) 16 g of \( CO \)
(D) 16 g of \( H_2 \)
A shopkeeper buys an item for Rs 2000 and marks it up by 50% to set the marked price. He then offers a 20% discount on the marked price. What is the profit earned by the shopkeeper?