1. In order to answer this one and the next one, we will use mass percentage as our guide, since every compound has a mass percentage for each element, and this is found by checking the total mass and the separate masses of each element, for example, MgF2, the mass percentage is 39% for Mg and 61% for F2, this is due to their molar mass, 24g for Mg and 38g for F2
We have 27.1 g of Mg, and this will always correspond for 39% of the total mass of the compound, so we can do the following math:
100% = x
39% = 27.1g
x = 69.5 grams is the total mass of MgF2, now we only have to subtract the value of Mg and then we will have F2
69.5 - 27.1 = 42.4 grams, this is the mass of Fluorine
2. The same step by step from the previous question, 36% of the total mass is Al and 64% is S, but this question has a little difference, now we have the mass of the compound, but the process is very similar
100% = 50.2 grams
64% = x grams
x = 32.1 grams, which can be considered as letter A