There are 2 moles of NA2SO4 present in 284.078 grams of NA2SO4. Why? Well, we already know here that there are 284.078 grams of NA2SO4. To find how many moles are present in this compound, we would have to divide these grams by the molar mass of the compound. When we go to the periodic table of elements, we will find that there are two moles sodium (which represents 45.98 grams), one mole sulfur (which represents 32.06 grams), and four moles oxygen (which represents 64 grams). When combining these, we would get one mole of sodium sulfate which is representative of 142.04 grams total. That is our molar mass. Now that we have the molar mass, we can go back and divide. 284.078 divided by 142.04 is equal to about 1.99999, and that rounds up to 2 moles. Hence, there are 2 moles of NA2SO4 present in 284.078 grams of NA2SO4.
Your final answer: A is your answer.