The question is in the photo (Sorry for being lazy lol )

• When Sodium Sulfate is mixed with Barium chloride, the following reaction occurs :

• a precipitate is the solid that forms, the white solide will be BaSO4

• So option 4 is correct. BaSo4.

The mass of NaCl : 50.5 g

The mole is the number of particles(molecules, atoms, ions) contained in a substance  

1 mol = 6.02.10²³ particles

Can be formulated

N=n x No

N = number of particles

n = mol

No = Avogadro's = 6.02.10²³

There are 5.20 x 10²³ units of NaCl, so mol NaCl :

Mass of NaCl(MW=71 g/mol) :