Atoms MCQ: Introduction & Explanation

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Atoms are the smallest and elementary unit of any ordinary matter. Every atom has a nucleus in the centre and one or more electrons revolving around it in energy shells. One or more protons and several neutrons make up the nucleus. The protons have a positive charge, while the electrons have a negative charge and the neutrons have none. The atom is electrically neutral if the number of protons and electrons is equal and thus nullifies each other.

Structure of atoms

Structure of Atom

When an atom contains more or fewer electrons than protons, it has a negative or positive overall charge accordingly and is called an ion. The electromagnetic force attracts electrons to its protons in the nucleus. The number of protons in the nucleus is the atomic number and it determines the chemical properties the atom belongs to.

The following are the five atomic models:

The atomic model of John Dalton -Solid Sphere model
The model of J.J. Thomson - Model of Plum Pudding
The model of Ernest Rutherford
The model of Niels Bohr
The model of Erwin Schrödinger - Quantum Model/Electron Cloud Model

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Related Topics
Properties of Matter	Atoms and Molecules	Difference between Elements and Compounds
Group 15 Elements	Group 16 Elements	Group 18 Elements
Redox Titration	Volumetric Analysis	SN2 Reaction
Solutions	Types of Solutions	Solubility

Multiple Choice Questions

Ques 1. Which of the following correctly represents the electronic distribution in the Mg atom?

(a) 3, 8, 1

(b) 2, 8, 2

(c) 1, 8, 3

(d) 8, 2, 2

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Ans. (b) 2, 8, 2

Explanation: Atomic number and the number of electrons in a magnesium atom is 12.

So, electronic configuration is 2, 8, 2 (as 12 = 2 + 8 + 2).

The maximum electrons on the K shell are 2 and the maximum electrons in the L shell are 8.

Ques 2. A sample of NH₃ molecules irrespective of source contains 82.35% Nitrogen and 17.65% of Hydrogen by mass. This data supports:

(a) Law of Conservation of Mass

(b) Law of Multiple Proportions

(c) Law of Definite Proportions

(d) Avogadro’s Law

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Ans. (c) Law of Definite Proportions

Explanation: According to the law of definite proportions, or ratio, the mass proportion of components in a compound's samples will always be the same.

The law of proportions, also known as the law of fixed constant, holds that the proportions of the constituent components that make up a chemical compound or composition will always be the same.

Ques 3. What is the molecular formula of potassium nitrate?

(a) KNO₃

(b) KNO

(c) KNO₂

(d) KON

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Ans. (a) KNO₃

Explanation: Potassium Nitrate is a crystalline salt with strong oxidizing powers. They are used in the manufacture of gunpowder, fertilizer, and in medicine. Potassium nitrate is the inorganic nitrate salt of potassium. K is the chemical representation of potassium and NO₃ is the chemical representation of nitrate.

Ques 4. Molecular mass is defined as the:

(a) Mass of one molecule of any substance compared with the mass of one atom of C – 12

(b) Mass of one atom in comparison with the mass of one atom of hydrogen

(c) Mass of one atom in comparison with the mass of one molecule

(d) None of the above

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Ans. (a) Mass of one molecule of any substance compared with the mass of one atom of C – 12

Explanation: The sum of all atoms' weight in a molecule is calculated using a scale with hydrogen, carbon, nitrogen, and oxygen atomic masses of 1, 12, 14, and 16, respectively. Water, for example, has a molecular mass of 18 (i.e. 2 + 16) since it contains two hydrogen atoms and one oxygen atom. Also known as molecular mass.

Ques 5. The number of moles in 46g of sodium with atomic number 23 is equal to.

(a) 4

(b) 2

(c) 0

(d) ½

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Ans. (b) 2

Explanation: It is given that,

Atomic Mass of Sodium or molar mass = 23

A number of moles in 46 g of Na is.

No. of moles = Given Mass/ Molar Mass

by substituting the value we get

No. of Moles = 46/23

No. of Moles = 2

Ques 6. Which of the following represents a correct chemical formula?

(a) CaCl

(b) BiPO₄

(c) NaSO₄

(d) NaS

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Ans. (b) BiPO₄

Explanation: BiPO4 is the only one of these compounds with the exact chemical formula. Bismuth orthophosphate is a compound containing bismuth. The valencies of all the elements are not satisfied in the other compounds. Calcium chloride (CaCl₂), sodium sulfate (Na₂SO₄), and sodium sulphide (Na₂S) are the correct chemical composition representations.

Ques 7. What is the formula mass unit of ZnO?

(a) 18 u

(b) 81 u

(c) 88 u

(d) 188 u

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Ans. (b) 81 u

Explanation: Atomic mass of Zn = 65u

Atomic mass of O = 16u

Calculating the formula unit masses of them:

ZnO = Zn + O

ZnO = (65 + 16)u = 81u

Ques 8. Atomic models have been improved over the years. Arrange the following atomic models in their chronological order

(i) Rutherford’s atomic model

(ii) Thomson’s atomic model

(ii) Bohr’s atomic model

(a) (i), (ii) and (iii)

(b) (ii), (iii) and (i)

(c) (ii), (i) and (iii)

(d) (iii), (ii) and (i)

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Ans: (c) (ii), (i) and (iii)

Explanation: The first atomic model was given by J.J. Thomson in 1904. A model of the atom with electrons revolving around the nucleus was proposed by Rutherford in 1911. The final atomic model with improvement came in 1915 by Bohr. The chronological order of the atomic models is (ii) Thomson’s atomic model (i) Rutherford’s atomic model (iii) Bohr’s atomic model.

Ques 9. How many atoms of oxygen are present in 300 grams of CaCO₃?

(a) 54.207 × 10²³

(b) 6.207 × 10²³

(c) 12.207 × 10²³

(d) 22.2 × 10²³

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Ans. (a) 54.207 × 10²³

Explanation: Given mass of CaCO₃= 300g

Molar mass of CaCO₃= 40 + 12 + (3 x 16) =100 g mol-¹

Number of moles of CaCO₃ = mass / molar mass

= 300g/ 100 g mol^-¹

= 3 moles

Number of oxygen atoms in CaCO₃ = 3

Number of moles of oxygen atoms = 3 x 3 moles = 9 moles

1 mole of oxygen contains 6.022 x 10²³ atoms of oxygen.

Therefore , 9 moles of oxygen contains = 9 x 6.022 x 10²³ atoms

=5.4 x 10²⁴ oxygen atoms.

Ques 10. Which of the following represents the correct relation between Avogadro's number (No), number of particles (N), and moles (n)?

(a) n = N / N_o

(b) n = N_o / N

(c) n = N N_o

(d) all are correct

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Answer. (a) n = N / No

Explanation: The correct relation between Avogadro’s number and the number of particles and moles is given by the formula, n = N / No where, No is the Avogadro’s number, n is the number of miles and N is the number of particles.

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Atoms MCQ: Introduction & Explanation

Multiple Choice Questions

CBSE CLASS XII Related Questions

2.
Two point charges \( q_1 = 16 \, \mu C \) and \( q_2 = 1 \, \mu C \) are placed at points \( \vec{r}_1 = (3 \, \text{m}) \hat{i}\) and \( \vec{r}_2 = (4 \, \text{m}) \hat{j} \). Find the net electric field \( \vec{E} \) at point \( \vec{r} = (3 \, \text{m}) \hat{i} + (4 \, \text{m}) \hat{j} \).

3.
A parallel plate capacitor has plate area \( A \) and plate separation \( d \). Half of the space between the plates is filled with a material of dielectric constant \( K \) in two ways as shown in the figure. Find the values of the capacitance of the capacitors in the two cases.

4.
The resistance of a wire at 25°C is 10.0 \( \Omega \). When heated to 125°C, its resistance becomes 10.5 \( \Omega \). Find (i) the temperature coefficient of resistance of the wire, and (ii) the resistance of the wire at 425°C.

Similar Physics Concepts

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Atoms MCQ: Introduction & Explanation

Multiple Choice Questions

CBSE CLASS XII Related Questions

2.Two point charges \( q_1 = 16 \, \mu C \) and \( q_2 = 1 \, \mu C \) are placed at points \( \vec{r}_1 = (3 \, \text{m}) \hat{i}\) and \( \vec{r}_2 = (4 \, \text{m}) \hat{j} \). Find the net electric field \( \vec{E} \) at point \( \vec{r} = (3 \, \text{m}) \hat{i} + (4 \, \text{m}) \hat{j} \).

3.A parallel plate capacitor has plate area \( A \) and plate separation \( d \). Half of the space between the plates is filled with a material of dielectric constant \( K \) in two ways as shown in the figure. Find the values of the capacitance of the capacitors in the two cases.

4.The resistance of a wire at 25°C is 10.0 \( \Omega \). When heated to 125°C, its resistance becomes 10.5 \( \Omega \). Find (i) the temperature coefficient of resistance of the wire, and (ii) the resistance of the wire at 425°C.

Similar Physics Concepts

Comments

SUBSCRIBE TO OUR NEWS LETTER

2.
Two point charges \( q_1 = 16 \, \mu C \) and \( q_2 = 1 \, \mu C \) are placed at points \( \vec{r}_1 = (3 \, \text{m}) \hat{i}\) and \( \vec{r}_2 = (4 \, \text{m}) \hat{j} \). Find the net electric field \( \vec{E} \) at point \( \vec{r} = (3 \, \text{m}) \hat{i} + (4 \, \text{m}) \hat{j} \).

3.
A parallel plate capacitor has plate area \( A \) and plate separation \( d \). Half of the space between the plates is filled with a material of dielectric constant \( K \) in two ways as shown in the figure. Find the values of the capacitance of the capacitors in the two cases.

4.
The resistance of a wire at 25°C is 10.0 \( \Omega \). When heated to 125°C, its resistance becomes 10.5 \( \Omega \). Find (i) the temperature coefficient of resistance of the wire, and (ii) the resistance of the wire at 425°C.