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Olympiad Test: Atoms and Molecules- 1 - Class 9 MCQ


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10 Questions MCQ Test Science Olympiad Class 9 - Olympiad Test: Atoms and Molecules- 1

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Olympiad Test: Atoms and Molecules- 1 - Question 1

The atomic theory of matter was proposed by

Detailed Solution for Olympiad Test: Atoms and Molecules- 1 - Question 1
The atomic theory of matter was proposed by John Dalton.

John Dalton (1766-1844) developed the first useful atomic theory of matter.

Olympiad Test: Atoms and Molecules- 1 - Question 2

The atoms of which of the following pair of elements are most likely to exist in free state?

Detailed Solution for Olympiad Test: Atoms and Molecules- 1 - Question 2
The atoms of which are most likely to exist in free state are Helium and neon being inert gases having octet filled.
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Olympiad Test: Atoms and Molecules- 1 - Question 3

Which of the following elements has the same molecular mass as its atomic mass?

Detailed Solution for Olympiad Test: Atoms and Molecules- 1 - Question 3
Neon is the element having same molecular mass as its atomic mass.

Actually, Neon would be listed as having an atomic mass of about 20.18, because of a mixture of isotopes, Z = Atomic number, the number of protons in the nucleus which defines the element.

Olympiad Test: Atoms and Molecules- 1 - Question 4

The atomic number of an element X is 13. What will be the number of electrons in its ion X3+?

Detailed Solution for Olympiad Test: Atoms and Molecules- 1 - Question 4
X ⟶ X3+ means it loses three electrons, so X3+ = 10 electrons.
Olympiad Test: Atoms and Molecules- 1 - Question 5

Kalium is the Latin name of

Detailed Solution for Olympiad Test: Atoms and Molecules- 1 - Question 5
Some symbols have been taken from the names of elements in Latin, German, or Greek. For example, symbol of potassium is K from its Latin name Kalium.
Olympiad Test: Atoms and Molecules- 1 - Question 6

Certain mass of carbon burns with a given mass of oxygen to form certain mass of carbon mass of carbon dioxide, which law of chemical combination is used in this process of formation of compound

Detailed Solution for Olympiad Test: Atoms and Molecules- 1 - Question 6
First, let us write the reaction taking place here

C + O2 → CO2

As per the given condition, when 3.0 g of carbon is burnt in 8.00 g oxygen, 11.00 g of carbon dioxide is produced.

3g + 8g →11 g ( from the above reaction)

The total mass of reactants = mass of carbon + mass of oxygen

=3g+8g

=11g

The total mass of reactants = Total mass of products

Therefore, the law of conservation of mass is proved.

Then, it also depicts that the carbon dioxide contains carbon and oxygen in a fixed ratio by mass, which is 3:8.

Thus it further proves the law of constant proportions.

3 g of carbon must also combine with 8 g of oxygen only.

This means that (50−8)=42g of oxygen will remain unreacted.

The remaining 42 g of oxygen will be left un-reactive. In this case also, only 11 g of carbon dioxide will be formed

The above answer is governed by the law of constant proportions.

Olympiad Test: Atoms and Molecules- 1 - Question 7

Which postulates of Dalton’s atomic theory gives laws of conservation of mass

Detailed Solution for Olympiad Test: Atoms and Molecules- 1 - Question 7
The postulate of Dalton’s atomic theory resulting from the law of conservation of mass is ‘The relative number and kinds of atoms are constant in a given compound. Atoms cannot be created nor destroyed in a chemical reaction’.
Olympiad Test: Atoms and Molecules- 1 - Question 8

In water, hydrogen and oxygen are present in the ratio of

Detailed Solution for Olympiad Test: Atoms and Molecules- 1 - Question 8
H2O = 2 : 16 = 1 : 8
Olympiad Test: Atoms and Molecules- 1 - Question 9

What is the mass of 0.2 mole of lead nitrate? (N=14, O=16, Pb=207)

Detailed Solution for Olympiad Test: Atoms and Molecules- 1 - Question 9

Gram Molecular weight of Pb(NO3)2

= 207 + (2 × 14) + 2 (16 × 3)

= 207 + 28 + 96

= 331

1 mole of Pb(NO3)2 is 331g

Therefore 0.2 mole of Pb(NO3)2 is 331 × 0.2

= 66.2 g

Olympiad Test: Atoms and Molecules- 1 - Question 10

Find the total percentage of oxygen in magnesium nitrate crystal i.e., Mg(No3)2.6H2O (Atomic weight : H = 1, N = 14, O = 16, Mg = 24)

Detailed Solution for Olympiad Test: Atoms and Molecules- 1 - Question 10

Molecular weight of Mg(NO3)2.6H2O

= 24 + 2 (14 + 16 × 3) + 6(2 × 1 + 16)

= 24 + 124 + 108 = 256 amu

Atomic mass of oxygen in Mg(NO3)2.6H2O is,

= 2(16 × 3 × 6(16) = 96 + 96 = 192

% of oxygen = 192/256 × 100 = 75%

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