Answer:
18.9 moles of MgCl2 = 17.834 kg of MgCl2
Step-by-step explanation:
The molecular weight of MgCl is 80.0 g/mol . So, to convert the given mole amount to grams, multiply this by this number, which is constant for all compounds with a specific composition (mass fraction).
Considering the original question was in the context of chemistry, I wanted to make it seem formal and more educational too. Hopefully that worked!
EDIT: Came up with some text around what happens inside cells that would have made it better if someone just had an issue converting units, but I doubt my answer will be accepted >.<