Answer:
m = 20.9 g.
Explanation:
Hello there!
In this case, according to the given information, it turns out possible for us to solve this problem by recalling both the Avogadro's number for the calculation of the moles in the given molecules of calcium phosphate and the molar mass of this compound in order to secondly calculate the mass as shown on the following setup:

Regards!
Valence électrons don’t define which group You are in so you can cross those choices out.
A would be incorrect because element 1 has 1 valence electron while element 2 has 2 valence electrons.
D would be correct because both elements have two valence electrons.
Also, pls don’t hate if I am wrong!