Atube of toothpaste contains 0.76 g of sodium monofluorophosphate(na2po3f)in 100 ml.
(a)what mass of florine atoms in mg was present?
(b) how many fluorine in atoms were present?

Explanation:

(a)   Molar mass of is 691.92 g/mol. And, there is 0.76 g of sodium monofluorophosphate () in 100 ml.

Molar mass of fluorine is 19 g/mol.

This means that in 691.92 g/mol there are 19 g/mol of fluorine is present. Hence, mass of fluorine present in 0.76 g is calculated as follows.

               Mass of fluorine =        

                                           = 0.021 g

As, 1 g = 1000 mg. Hence, 0.021 g = 21 mg.

Therefore, mass of florine atoms in present was 21 mg.

(b)    As we know that number of moles equal mass divided by molar mass.

Therefore,      No. of moles of fluorine =

                                         =  

                                          = 0.001 mol

Hence, according to mole concept in one mole there are atoms.

So, in 0.001 mole number of fluorine atoms will be calculated as follows.

                  atoms.

                 = atoms

Therefore, there are atoms of fluorine were present.

4d^55s^1 ( third choice)