Atomic mass of sulphur = 32 amu
Gram atomic mass of sulphur = 32 g
1 mole of sulphur contains  = 6.023 x 10²³ atoms
Now 32 g of sulphur contains
                            = 6.023 x 10²³ atoms
3.2 g of sulphur would contain

      
   
Gram atomic mass of calcium  = 40 g
    1 mole of calcium  = 40 g
                               = 6.023 x 10²³ atoms
Now 6.023 x 10²³ atoms of calcium have mass  = 40 g

Significant figures are meaningful digits which are known with certainty. 

Four

Two