Question

calculate the number of moles in 71g of chlorine( mass of cl is 35.5u)

Answer 1

No. of moles = Given mass / molar mass * 6.022*10^23
= 71 /35.5 * 6.022*10^23
= 1.2044 * 10 ^ 24

Answer 2

1 mole of atom = gram atomic mass
so, 1 mole of chlorine atoms = gram atomic mass of chlorine
now,   35.5g of chlorine = 1 mole of chlorine
            71g of chlorine = 1 divide by 35.5 x 71
                                     = 2 moles