Atoms and Molecules Test

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Atoms and Molecules Test - 16

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Weekly Quiz Competition

Question 1

1 / -0

Use the following information to answer the next question.

During the 17^th and the 18^th centuries, a few chemists investigated chemical changes quantitatively. By conducting reactions in closed containers, they showed that the products of a chemical change had the same mass as the reactants but the properties of the compounds, before and after the reaction, changed.

The above observation illustrates that, before and after the reaction, the mass of the system is

not conserved and the nature of the compounds does not change.

conserved and the nature of the compounds changes.

conserved but the nature of the compounds does not change.

not conserved but the nature of the compounds changes.

Solution

According to the law of conservation of mass, mass can neither be created nor be destroyed and remains conserved before and after a chemical reaction. The nature of the compounds, before and after the reaction, changes due to change in the properties of the atoms.

The correct answer is B.

Question 2
1 / -0

Use the following information to answer the next question.

The molecular mass of a substance is the sum of atomic masses of various atoms present in one formula. The molecular mass of a compound X is 44.

The compound X is

A
CO

B
C₂O

C
CO₂

D
C₂O₂

Solution

Here, the student is required to know the calculation for molecular mass of various compounds.

Atomic mass of C = 12 and atomic mass of O = 16

∴ CO₂ = 12 + (2 × 16) = 44.

The correct answer is C.

Why alternative A is wrong:

Molecular mass of CO will be 12 + 16 = 28. Thus, this alternative is incorrect.

Why alternative B is wrong:

Molecular mass of C₂O will be (2 ×12) + 16 = 40. Thus, this alternative is incorrect.

Why alternative D is wrong:

Molecular mass of C₂O₂ will be (2 ×12) + (2 ×16) = 56. Thus, this alternative is incorrect.

Question 3

1 / -0

Use the following information to answer the next question.

During the chemical reaction between carbon disulfide and oxygen gas, carbon dioxide and sulfur dioxide are yielded. The reaction proceeds with rearrangement of atoms to form different products.

The product sulfur dioxide is formed by combination of sulfur and oxygen, respectively, in the ratio of

2:1

1:2

2:3

3:2

Solution

As the name suggests, sulfur dioxide consist of one atom of sulfur and two atoms of oxygen, thereby making the ratio as 1:2.

The correct answer is B.

Why alternative A is wrong:

The ratio 2:1 implies that an atom of sulfur dioxide (SO₂) contains two atoms of sulfur and one atom of oxygen, which is not true.

Why alternative C is wrong:

The ratio 2:3 implies that an atom of sulfur dioxide (SO₂) contains two atoms of sulfur and three atoms of oxygen, which is not true.

Why alternative D is wrong:

The ratio 3:2 implies that an atom of sulfur dioxide (SO₂) contains three atoms of sulfur and two atoms of oxygen, which is not true.

Question 4
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How many atoms are present in a phosphorous molecule?

A
One

B
Two

C
Three

D
Four

Solution

A phosphorus molecule is a tetravalent molecule that contains four phosphorous atoms.

The correct answer is D.

Why alternatives A, B and C are wrong:

A phosphorus molecule contains four atoms of phosphorus. Hence, alternatives A, B, and C are incorrect.
Question 5
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Which of the following elements exists as a monatomic molecule?

A
Hydrogen

B
Nitrogen

C
Oxygen

D
Boron

Solution

Boron is located on the top 13^th group of the periodic table, which lies in the middle of a period, and is chemically inert to almost all of the other elements. Hence, boron exists as a monatomic molecule.

The correct answer is D.

Why alternative A is wrong:

Hydrogen is the first element in the periodic table. It lies in the first period and in the first group. It is very reactive and hence, cannot occur as a monatomic molecule.

Why alternative B is wrong:

Nitrogen is in the 15^th group of the second period of the periodic table. It is a reactive non-metal and cannot occur as a monatomic molecule.

Why alternative C is wrong:

Oxygen is in the 16^th group of the second period of the periodic table. It is a very reactive non-metal and cannot occur as a monatomic molecule.
Question 6
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When one atom of carbon combines with two atoms of sulfur, the product formed is

A
CS

B
C₂S

C
CS₂

D
C₂S₂

Solution

When one atom of carbon combines with two atoms of sulfur, the chemical reaction can be represented as

C + S₂ → CS₂

Hence, the product formed is carbon disulfide (CS₂).

Hence, the correct answer is option C.
Question 7
1 / -0

Use the following information to answer the next question.

John Dalton, an English school teacher, put forth the theory of atoms based on chemical laws of combinations.

Which of the following statements is not a postulate of Dalton’s theory?

A
Atoms cannot be created or destroyed.

B
Atoms are extremely tiny invisible particles.

C
Atoms combine in complex fractional ratios.

D
All the atoms of a particular element have identical properties.

Solution

The fourth postulate of Dalton’s theory states that atoms combine in simple whole number ratios and not in complex fractional ratios

The correct answer is C.
Question 8
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Atoms combine to form molecules in

A
multiple proportions

B
fractional proportions

C
definite proportions

D
indefinite proportions

Solution

A molecule is formed when atoms of different or same elements join in definite proportions.

Hence, the correct answer is option C.

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Atoms and Molecules Test - 16

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Question 1

not conserved and the nature of the compounds does not change.

conserved and the nature of the compounds changes.

conserved but the nature of the compounds does not change.

not conserved but the nature of the compounds changes.

Solution

Question 2

CO

C2O

CO2

C2O2

Solution

Question 3

2:1

1:2

2:3

3:2

Solution

Question 4

One

Two

Three

Four

Solution

Question 5

Hydrogen

Nitrogen

Oxygen

Boron

Solution

Question 6

CS

C2S

CS2

C2S2

Solution

Question 7

Atoms cannot be created or destroyed.

Atoms are extremely tiny invisible particles.

Atoms combine in complex fractional ratios.

All the atoms of a particular element have identical properties.

Solution

Question 8

multiple proportions

fractional proportions

definite proportions

indefinite proportions

Solution

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C₂O

CO₂

C₂O₂

C₂S

CS₂

C₂S₂