The graph shows the typical test result of a property of a building material. Identify the test and the variables represented on the X-axis and Y-axis from the given options.
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 \( H_2 \)