Question

Calculate number of molecules present in One drop of water having mass 0.05 grams.
please friends I need it urgently !

Answer 1

Molecular mass of water = 18 g
no . of molecules in 0.05 g of water = 0.05/18 = 2.78 × 10⁻³ molecules
 one molecule = 6.023 × 10²³ molecules
Therefore ,
2.78 × 10⁻³ molecule of water contains = 2.78 × 10⁻³ × 6.023 × 10²³ molecules = 1.67 × 10²¹ molecules .

Answer 2

Hi Friend
________
1 Mole = 18 grams = 6.022 x 10^23 molecules
1 gram = 6.022 x 10^23/18 molecules
5/100 grams = 6.022   x 10 ^23 /18 X 5/100 molecules 
                     = 6.022 x 10 ^21/18 X 5
                     = 30.11 x 10 ^ 21 /18
                     =1.67 x 1^21 molecules.