Question

The number of atoms in 6 amu of He is ____. 

(A) 18 

(B) 18 x 6.022 x 10²³ 

(C) 54 

(D) 54 x 6.023 x 10²³

Answer 1

Correct option: (A) 18 

mass of one atom = \(\cfrac{1}{12}\) x Atomic mass amu

mass of 1 He atom = \(\cfrac{1}{12}\) x 4 = \(\cfrac{1}{4}\) amu

∴ mass of x He atoms = 6 amu

∴ x = 6 x 3 = 18 atoms.

Comments

amu of one atom =  1/12 x Atomic mass amu
amu  of 1 He atom =  1/12 x 4 =  1/3 amu
               amu      :    no of atoms
                1/3 amu                 1
                6 amu                     X

                   X/3= 1x6
                   X= 3 x6 =18 atoms