What is the mass of a drop of ethanol containing 3.90 x 10^22 c2h5oh molecules

mass = 2.97896 grams

Explanation:
number of molecules = number of moles * Avogadro's number
We are given that:
number of molecules = 3.9 * 10^22
Avogadro's number = 6.022 * 10^23
Therefore, we can get the number of moles as follows:
3.9 * 10^22 = number of moles * 6.022 * 10^23
number of moles = 0.06476 moles

Now, from the periodic table:
mass of carbon = 12 grams
mass of hydrogen = 1 gram
mass of oxygen = 16 grams
This means that:
mass of one mole of ethanol = 2(12) + 5(1) + 16 + 1 = 46 grams

Finally, we will get the mass of the sample as follows:
number of moles = mass / molar mass
We have:
number of moles = 0.06476 moles
molar mass = 46 grams
Therefore:
0.06476 = mass / 46
mass = 2.97896 grams

Hope this helps :)