I think i explained number 12 in a different thread. For number 6 the only answer that divides evenly into all of the values is 19. If you think about the formula for a compound the number of moles of each element should be a whole number. So you should multiply the average atomic mass by a whole number. None of the other choices divide evenly into all of the numbers. The question is just saying that the mass of Q in different compounds has this much mass so first the first it would be Q(2) because 19 times 2 equals 38. The second would be Q(3) 19*3=57 and so on.

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