# Bell metal contains 80% copper the mass of bell metal which contains 1.5 x 1020 atoms of copper is

If 6.022 × 10²³ atoms = 1 mole

Then, moles of Cu  = 1.5 x 1020/6.022 × 1023  = 0.00025 moles

Mass of Cu in coin = = 0.00025 mol × 64g/mol  = 0.016 g

Therefore 1.5 x 1020 atoms of copper has a mass of 0.016 g.

This 80% of the piece of metal, weight of the mass is 100%  = 100/80 x 0.016 = 0.02 g

The piece of metal has a mass of 0.02g

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