NCERT Exemplar · Class 9 · Science

Chapter 3: Atoms and Molecules

Practice each question, then open the answer or worked solution.

Explanation:

2 questions

Q8Written answer

Mass of one atom of oxygen is

a) 16/ 6.023 × 10²³g

b) 32/ 6.023 × 10²³g

c) 3/ 6.023 × 10²³g

(d) 8u

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Worked solution

Answer is (a) 16/ 6.023 × 10²³g

Explanation:

Mass of one atom of oxygen = Atomic mass/NA = 16/ 6.023 × 10²³g

Note: NA = 6.023×10²³

Q9Written answer

3.42 g of sucrose are dissolved in 18g of water in a beaker. The number of oxygen atoms in the solution are

(a) 6.68 × 10²³ (b) 6.09 × 10²² (c) 6.022 × 10²³ (d) 6.022 × 10²¹

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Worked solution

Answer is (a) 6.68 × 10²³