How many fluroine atoms are present in 5.62 g of c2f4 ?

Molar mass of C= 12g/mol
2C= 2*12g/mol= 24g/mol
Molar Mass of F=19g/mol
4F= 4*19g/mol= 76g/mol
Total molar mass of C2F4 = (24g/mol+76g/mol)= 100g/mol

Now you need to find the moles of Fluorine
Moles= Mass/molar mass
Moles of Fluorine = 5.62g/100g/mol=0.0562mol of Fluorine

To find the number of atoms you multiply moles by Avogadro's number( atoms )

So the number of Fluorine atoms= 0.0562* 6.022x10^23= 3.38x10^22 atoms or  atoms