# 10 - Science - 10. Chemistry – Atoms And Molecules

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• 1.

### From the given examples, form the pair of isotopes.   18 Ar 40, 17 Cl 35, 20 Ca 40, 17 Cl 37

• A.

18 Ar 40, 20 Ca 40

• B.

17 Cl 35, 17 Cl 37

B. 17 Cl 35, 17 Cl 37
Explanation
The pair of isotopes in the given examples is 17 Cl 35 and 17 Cl 37. Isotopes are atoms of the same element that have different numbers of neutrons. In this case, both atoms are chlorine (Cl) atoms, but one has 35 neutrons and the other has 37 neutrons.

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• 2.

### From the given examples, form the pair of isobars.   18 Ar 40, 17 Cl 35, 20 Ca 40, 17 Cl 37

• A.

17 Cl 35, 17 Cl 37

• B.

18 Ar 40, 20 Ca 40

B. 18 Ar 40, 20 Ca 40
Explanation
Isobars are atoms or ions that have the same atomic mass but different atomic numbers. In the given examples, the pair 18 Ar 40 and 20 Ca 40 form isobars because they have the same atomic mass of 40 but different atomic numbers of 18 and 20 respectively. Therefore, the correct answer is 18 Ar 40, 20 Ca 40.

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• 3.

### Molecular mass of nitrogen is 28. Its atomic mass is 14. Find the atomicity of nitrogen.

• A.

28

• B.

14

• C.

2

• D.

3

C. 2
Explanation
The atomicity of nitrogen is 2 because its molecular mass is 28, which is twice its atomic mass of 14. This means that nitrogen exists as a diatomic molecule, with two nitrogen atoms bonded together.

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• 4.

### Gram molecular mass of oxygen is 32g. Density of oxygen is 1.429g/cc. Find the gram molecular volume of oxygen.

• A.

1.429g/cc

• B.

32g

• C.

1 lit

• D.

22.4 lit

D. 22.4 lit
Explanation
The gram molecular volume of oxygen is 22.4 liters. This is because the given information states that the gram molecular mass of oxygen is 32g and the density of oxygen is 1.429g/cc. By using the conversion factors provided (1.429g/cc, 32g, 1 lit, and 22.4 lit) and performing the necessary calculations, we arrive at the answer of 22.4 liters.

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• 5.

### Calculate the gram molecular mass of water from the values of gram atomic mass of hydrogen and of oxygen.

• A.

1

• B.

16

• C.

18

• D.

19

C. 18
Explanation
The gram molecular mass of water can be calculated by adding the gram atomic mass of hydrogen (1) to the gram atomic mass of oxygen (16). Therefore, the gram molecular mass of water is 18.

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• 6.

### One mole of any substance contains 6.023 x 1023 particles. If 3.0115 x 1023  particles are present in CO2. Find the number of moles.

• A.

1

• B.

2

• C.

.05

• D.

0.25

C. .05
Explanation
The given question states that one mole of any substance contains 6.023 x 10^23 particles. Therefore, to find the number of moles, we divide the given number of particles (3.0115 x 10^23) by the number of particles in one mole. This calculation gives us 0.05 moles.

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• Mar 22, 2023
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