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NCERT Exemplar Solutions Class 9 Science Solutions for Atoms and Molecules - Exercise in Chapter 3 - Atoms and Molecules

Question 39 Atoms and Molecules - Exercise

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

Answer:

one gram of gold sample will contain 90/100 = 0.9g of gold

number of moles of gold = mass of gold / atomic mass of gold

= 0.9/19.7 = 0.0046

one mole of gold contains NA atoms = 6.022 × 1023

Therefore, 0.0046 mole of gold will contain = 0.0046 × 6.022

= 2.77 × 1021

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