Chemistry MCQs

Question #521

Share Report

The number of neutrons in an atom with atomic number 17 and mass number 35 is:

A. 18

B. 17

C. 35

D. 52

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option A

Explanation:
The atomic number (Z) equals the number of protons, which is 17. The mass number (A) is the sum of protons and neutrons. Therefore, the number of neutrons = A - Z = 35 - 17 = 18. This atom is Chlorine-35, a stable isotope of chlorine.

This question belongs to: Science chemistry

Question #522

Share Report

Which of the following was proposed by Rutherford's alpha-particle scattering experiment?

A. Electrons exhibit wave-particle duality.

B. Electrons revolve in fixed energy orbits.

C. The atom is a positively charged sphere with embedded electrons.

D. Most of the mass and positive charge is concentrated in a tiny nucleus.

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
Rutherford's experiment led to the nuclear model of the atom, concluding that almost all the mass and positive charge are concentrated in a very small central nucleus, while electrons orbit around it. Option B is Thomson's model, A is Bohr's model, and D is de Broglie's concept.

This question belongs to: Science chemistry

Question #523

Share Report

The maximum number of electrons that can be accommodated in the N shell is:

A. 50

B. 18

C. 8

D. 32

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
The maximum number of electrons in a shell is given by the formula 2n², where n is the principal quantum number. For the N shell, n = 4. Thus, maximum electrons = 2(4)² = 2(16) = 32. The K, L, M, and N shells hold 2, 8, 18, and 32 electrons respectively.

This question belongs to: Science chemistry

Question #524

Share Report

Which of the following pairs represents isobars?

A. Hydrogen and Deuterium

B. Argon-40 and Calcium-40

C. Carbon-12 and Carbon-14

D. Chlorine-35 and Chlorine-37

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
Isobars are atoms of different elements with the same mass number but different atomic numbers. Argon (Z=18) and Calcium (Z=20) both have a mass number of 40, making them isobars. Options A, B, and D are isotopes, as they represent the same element with different mass numbers.

This question belongs to: Science chemistry

Question #525

Share Report

The valency of an element with atomic number 13 is:

A. 1

B. 4

C. 3

D. 2

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
The element with atomic number 13 is Aluminum. Its electronic configuration is 2, 8, 3. Since it has 3 electrons in its outermost shell, it loses these 3 electrons to achieve a stable octet configuration, making its valency 3. It forms Al³⁺ ions in chemical compounds.

This question belongs to: Science chemistry

Question #526

Share Report

An ion M³⁺ has 10 electrons and 14 neutrons. The atomic number and mass number of M are:

A. 10 and 27

B. 10 and 24

C. 13 and 24

D. 13 and 27

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
The ion M³⁺ has lost 3 electrons, so the neutral atom M has 10 + 3 = 13 electrons. Thus, the atomic number is 13. The mass number is protons + neutrons = 13 + 14 = 27. The element is Aluminum, and the specific isotope is Aluminum-27.

This question belongs to: Science chemistry

Question #527

Share Report

Which of the following statements about cathode rays is incorrect?

A. They are made up of electrons.

B. They are deflected by magnetic and electric fields.

C. Their nature depends on the gas used in the discharge tube.

D. They travel in straight lines.

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
Cathode rays consist of electrons, which are fundamental particles. Therefore, their nature (charge to mass ratio) is independent of the gas used in the cathode ray tube or the material of the cathode. All other statements are correct properties of cathode rays, demonstrating their fundamental particle nature.

This question belongs to: Science chemistry

Question #528

Share Report

Bohr's atomic model fails to explain the spectrum of:

A. Hydrogen atom

B. Lithium ion (Li²⁺)

C. Multi-electron atoms

D. Helium ion (He⁺)

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
Bohr's model successfully explains the spectrum of hydrogen and hydrogen-like species (single electron systems like He⁺, Li²⁺). However, it fails to explain the spectra of multi-electron atoms due to electron-electron repulsions and cannot account for the splitting of spectral lines in magnetic (Zeeman) and electric (Stark) fields.

This question belongs to: Science chemistry

Question #529

Share Report

The discovery of the neutron was made by:

A. J.J. Thomson

B. John Dalton

C. Ernest Rutherford

D. James Chadwick

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
James Chadwick discovered the neutron in 1932 by bombarding beryllium with alpha particles, which emitted a highly penetrating radiation consisting of neutral particles with mass similar to protons. Thomson discovered the electron, Rutherford the proton, and Dalton proposed the foundational atomic theory of matter.

This question belongs to: Science chemistry

Question #530

Share Report

An ionic bond is formed by the:

A. Pooling of electrons

B. Sharing of electrons

C. Mutual sharing of electrons

D. Complete transfer of electrons

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
An ionic (electrovalent) bond is formed by the complete transfer of one or more electrons from a metal to a non-metal, resulting in the formation of oppositely charged ions which are held together by strong electrostatic forces. Sharing of electrons forms covalent bonds, while pooling describes metallic bonds.

This question belongs to: Science chemistry

Question #531

Share Report

Which of the following compounds contains a coordinate covalent bond?

A. H₂O

B. NH₄⁺

C. NaCl

D. Cl₂

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
In the ammonium ion (NH₄⁺), the nitrogen atom in ammonia (NH₃) shares its lone pair of electrons with a hydrogen ion (H⁺) which has no electrons. This type of bond, where both shared electrons are donated by a single atom, is a coordinate covalent (dative) bond.

This question belongs to: Science chemistry

Question #532

Share Report

Which of the following is a characteristic property of ionic compounds?

A. They are good conductors of electricity in the solid state.

B. They have low melting and boiling points.

C. They are soluble in non-polar solvents like benzene.

D. They are soluble in water and conduct electricity in molten or aqueous state.

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
Ionic compounds are soluble in polar solvents like water. In the solid state, ions are fixed in a lattice and cannot move, so they don't conduct. However, in molten or aqueous states, the ions become free to move, allowing them to conduct electricity. They generally have high melting points.

This question belongs to: Science chemistry

Question #533

Share Report

A covalent compound is generally formed between:

A. Two non-metals

B. Two metals

C. A noble gas and a metal

D. A metal and a non-metal

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option A

Explanation:
Covalent bonds are formed by the sharing of electrons, which typically occurs between two non-metal atoms that have high electronegativities and a tendency to gain electrons. Metals tend to lose electrons, forming ionic bonds with non-metals. Noble gases are generally inert and do not form bonds.

This question belongs to: Science chemistry

Question #534

Share Report

Which of the following molecules has a double covalent bond?

A. O₂

B. Cl₂

C. N₂

D. H₂

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option A

Explanation:
In an oxygen molecule (O₂), each oxygen atom has 6 valence electrons and needs 2 more to complete its octet. They share two pairs of electrons, forming a double covalent bond (O=O). H₂ and Cl₂ have single bonds, while N₂ has a triple covalent bond (N≡N).

This question belongs to: Science chemistry

Question #535

Share Report

Assertion (A): Covalent compounds generally have low melting points. Reason (R): The intermolecular forces in covalent compounds are weak compared to ionic compounds.

A. A is false but R is true.

B. Both A and R are true and R is the correct explanation of A.

C. A is true but R is false.

D. Both A and R are true but R is NOT the correct explanation of A.

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
Covalent compounds consist of molecules held together by weak van der Waals forces, unlike the strong electrostatic forces in ionic lattices. Therefore, less heat energy is required to break these intermolecular forces, resulting in low melting and boiling points. Both statements are true and R correctly explains A.

This question belongs to: Science chemistry

Question #536

Share Report

The chemical formula of calcium phosphate is:

A. Ca(PO₄)₂

B. Ca₂(PO₄)₃

C. CaPO₄

D. Ca₃(PO₄)₂

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
Calcium (Ca) has a valency of +2, and the phosphate ion (PO₄) has a valency of -3. To balance the charges, we need three calcium ions and two phosphate ions, giving the formula Ca₃(PO₄)₂. This is determined by criss-crossing the valencies of the constituent ions.

This question belongs to: Science chemistry

Question #537

Share Report

Which of the following compounds is electron-deficient?

A. NH₃

B. CH₄

C. H₂O

D. BF₃

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
In BF₃, boron has 3 valence electrons and forms 3 covalent bonds with fluorine, resulting in only 6 electrons in its valence shell. It does not complete its octet, making it an electron-deficient molecule and a strong Lewis acid. NH₃, H₂O, and CH₄ all have complete octets.

This question belongs to: Science chemistry

Question #538

Share Report

Which of the following molecules is non-polar?

A. HCl

B. NH₃

C. H₂O

D. CO₂

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
CO₂ is a linear molecule (O=C=O). Although the C=O bonds are polar, the molecule is symmetric, and the dipole moments of the two bonds are equal and opposite, canceling each other out. Thus, the net dipole moment is zero, making it non-polar. HCl, H₂O, and NH₃ are polar.

This question belongs to: Science chemistry

Question #539

Share Report

The modern periodic table is based on the:

A. Density of the elements

B. Atomic mass of the elements

C. Number of neutrons

D. Atomic number of the elements

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
The modern periodic law states that the physical and chemical properties of elements are periodic functions of their atomic numbers. This was proposed by Henry Moseley, correcting Mendeleev's periodic table which was based on atomic mass. Atomic number determines the electronic configuration and thus chemical properties.

This question belongs to: Science chemistry

Question #540

Share Report

Elements in the same group of the periodic table have the same:

A. Number of valence electrons

B. Atomic radius

C. Number of shells

D. Atomic mass

View Answer & Solution Discuss

Get Complete Subject PDF for Science

Correct Answer: Option A

Explanation:
Elements in the same vertical column (group) have the same number of electrons in their outermost shell (valence electrons). This gives them similar chemical properties. The number of shells increases as we go down a group, leading to trends in atomic radius and ionization energy.

This question belongs to: Science chemistry

Practice Questions

More Science Topics