Answer:
See below.
Step-by-step explanation:
Lets set up an example:
Mass of Na is 39.34 grams
Mass of Cl is 60.67 grams
What is the empirical formula?
The empirical formula is the smallest whole number ratio of moles of the elements present. We have 100 grams of the sample, with only sodium and chlorine with the indicated masses. The masses don't tell us the element count. That is, how many Na and Cl are in the sample? By converting the masses into moles, we can find the actual number of atoms in each.
Divide each mass by the molar mass of that element:
Na: (39.34 grams)/(23 g/mole) = 1.7 moles Na atoms
Cl: (60.67 grams)/(35.5 g/mole) = 1.7 moles Cl atoms
Both Na and Cl have the same numbers of atoms: (1.7 moles)*(6.02 x 10^23 atoms/mole) = a large number, but we don't need to calculate it since the mole unit eliminates the need for lots of zeros and calculator errors.
1 Na for every 1 Cl
The empirical formula is NaCl (but you probably suspected that from the start. It is an empirical formula because we can't know at this point if the actual formula my by multiples of the basic formula. E.g., it could also be Na2Cl2, Na3Cl3, and so on. All we know for certain is the the ratio of Na to Cl is 1:1.
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Having these steps in mind, let's look at the question and options.
A. Options
1: The molecular formula. [Don't have the data]
2: The smallest whole number ratio of moles. That's the goal we set.
3: The atomic number. [Later]
4: The density of the compound. [No difference]
B. Then, choose...
Option 1: The atomic masses of the elements. The atomic masses of each element will allow us the calculate the moles of each element.
Option 2: The molar mass of the compound. [Not needed and unknown]
Option 3: The chemical formula. [Then we'd be done already. No fun in that]
Option 4: The color of the compound. [No difference what she's wearing]
C. Then, choose...
Option 1: The number of electrons. [No difference]
Option 2: The valence electrons. [No difference]
Option 3: The number of protons. [No difference]
Option 4: The number of moles. Yes, we want the actual number of atoms for each element.
D. Finally, choose...
Option 1: The chemical bond type. [No difference]
Option 2: The empirical formula. Yes, we can take the ratio of the atoms from above and find the closest whole number ratio between them.
Option 3: The boiling point. [No difference]
Option 4: The molecular weight. [unavailable since we don't know the compound yet]
Congratulations