NCERT Solution: Atoms and Molecules

Long Answer Type

A gold sample contains 90% of gold and the rest copper. How many atoms of gold are present in one gram of this sample of gold?

One gram of gold sample will contain 90 /100 = 0.9  gram of gold 

Number of moles of gold =mass of gold / atomic mass of gold

0.9 / 197 = 0.0046
One moles of gold contains NA atoms = 6.022 x 1023
∴0.0046 mole of gold will contain = 0.0046  x 6.022 x 1023
= 2.77 x 1021 


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