Atomic Structure

Total Questions: 39

21. Which of the following particles has zero charge? [U.P. P.C.S. (Pre) 2012]

(a) Positron
(b) Neutrino
(c) Electron
(d) α-particle

Correct Answer: (b) Neutrino

Solution:A neutrino is a subatomic particle that is very similar to an electron, but has no electrical charge and a very small mass, which might even be zero. Neutrinos are one of the most abundant particles in the universe. Because they have very little interaction with matter, however, they are incredibly difficult to detect.

22. The alpha particle carries two positive charges. Its mass is very nearly equal to that of – [I.A.S. (Pre) 1996]

(a) Two protons.
(b) Nucleus of an atom of helium.
(c) Sum of masses of two positrons and two neutrons.
(d) Two positrons, as each positron carries a single positive charge.

Correct Answer: (b) Nucleus of an atom of helium.

Solution:An alpha particle is a fast-moving particle containing two protons and two neutrons (a helium nucleus). Its mass is equal to that of helium atom's nucleus. Alpha particles carry a charge of +2 and strongly interact with matter. Produced during alpha decay, alpha particles can travel only a few inches through the air and can be easily stopped with a sheet of paper.

23. The Nucleus of Helium has – [R.A.S/R.T.S. (Pre) 1996]

(a) Only one neutron
(b) Two protons
(c) Two protons and two neutrons
(d) One proton and two neutrons

Correct Answer: (c) Two protons and two neutrons

24. Which of the following elements does not contain neutrons? [64th B.P.S.C. (Pre) 2018]

(a) Oxygen
(b) Nitrogen
(c) Hydrogen
(d) Copper
(e) None of the above/More than one of the above

Correct Answer: (c) Hydrogen

Solution:

The atomic number of Hydrogen is 1. The Protium () isotope of hydrogen has no neutron, while Deuterium (1H²) has one neutron, and Tritium (1H³) has two neutrons.

25. Which of the following carries a negative charge? [45th B.P.S.C. (Pre) 2002]

(a) X-rays
(b) Alpha particles
(c) Beta particles
(d) Gamma rays

Correct Answer: (c) Beta particles

Solution:Beta particles (

β\beta

) are highly energetic electrons which are negatively charged (-1e). X-rays and Gamma rays are electromagnetic radiations and do not carry any charge, while Alpha particles are positively charged.

26. Which among the following is a positively charged particle emitted by a radioactive element? [68th B.P.S.C. (Pre) 2022]

(a) Cathode ray
(b) Beta ray
(c) Alpha ray
(d) More than one of the above
(e) None of the above

Correct Answer: (c) Alpha ray

Solution:Alpha particles (

α\alpha

) are positively charged particles emitted by radioactive elements, such as the Helium nucleus (

27. In an atom, the order of filling up of the orbitals is governed by: [I.A.S. (Pre) 2001]

(a) Aufbau's principle
(b) Heisenberg's uncertainty principle
(c) Hund's rule
(d) Pauli's exclusion principle

Correct Answer: (a) Aufbau's principle

Solution:

The Aufbau principle is used to determine the electron configuration of an atom, molecule, or ion. Electrons fill orbitals starting at the lowest available energy levels before filling higher ones.

28. Regarding the atom of a chemical element, the magnetic quantum number refers to: [I.A.S. (Pre) 2003]

(a) Orientation
(b) Shape
(c) Size
(d) Spin

Correct Answer: (a) Orientation

Solution:

The magnetic quantum number refers to the orientation of an electron's angular momentum around a given axis. It denotes the unique quantum state and the energy levels within a subshell.

Principal quantum number (n): Determines the size and energy level of an electron's orbital. Higher values of n indicate larger orbitals and higher energy levels.

Angular momentum or azimuthal quantum number (l): Determines the shape of an electron's orbital and has values ranging from 0 to n-1. Different values of l correspond to different subshells (s, p, d, f, etc.).

Magnetic quantum number ( $m l$ ): Determines the orientation of an electron's orbital in space. For a given value of l, $m_{l}$ can take integer values from -l to +l, including 0. This means that for a p subshell (l=1), there are three possible orientations ( $m$ = -1, 0, +1), corresponding to the $p x$ , $p y$ , and $p z$ orbitals.

Spin quantum number ( $m$ ): Describes the intrinsic angular momentum of an electron, which is also quantized and is often referred to as "spin up" (+1/2) or "spin down" (-1/2).

29. The number of electrons and neutrons in an element is 18 and 20, respectively. Its mass number is: [65th B.P.S.C. (Pre) 2019]

(a) 22
(b) 2
(c) 38
(d) 20
(e) None of the above/More than one of the above

Correct Answer: (c) 38

Solution:The mass number is the sum of protons and neutrons. Given 18 electrons = 18 proton( for neutral atom) and 20 neutrons, the mass number is

30. What is the mass number of an element, the atom of which contains two protons, two neutrons, and two electrons? [43rd B.P.S.C. (Pre) 1999]

(a) 2
(b) 4
(c) 6
(d) 8

Correct Answer: (b) 4

Solution:The mass number is the sum of protons and neutrons. Given two protons and two neutrons, the mass number is

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Atomic Structure

21. Which of the following particles has zero charge? [U.P. P.C.S. (Pre) 2012]

22. The alpha particle carries two positive charges. Its mass is very nearly equal to that of – [I.A.S. (Pre) 1996]

23. The Nucleus of Helium has – [R.A.S/R.T.S. (Pre) 1996]

24. Which of the following elements does not contain neutrons? [64th B.P.S.C. (Pre) 2018]

25. Which of the following carries a negative charge? [45th B.P.S.C. (Pre) 2002]

26. Which among the following is a positively charged particle emitted by a radioactive element? [68th B.P.S.C. (Pre) 2022]

27. In an atom, the order of filling up of the orbitals is governed by: [I.A.S. (Pre) 2001]

28. Regarding the atom of a chemical element, the magnetic quantum number refers to: [I.A.S. (Pre) 2003]

29. The number of electrons and neutrons in an element is 18 and 20, respectively. Its mass number is: [65th B.P.S.C. (Pre) 2019]

30. What is the mass number of an element, the atom of which contains two protons, two neutrons, and two electrons? [43rd B.P.S.C. (Pre) 1999]

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