Atomic Structure

Total Questions: 39

31. The mass number of a nucleus is: [67th B.P.S.C. (Pre) 2022]

Correct Answer: (a) The sum of the numbers of neutrons and protons
Solution:The mass number is the sum of the total number of protons and neutrons inside a nucleus and represents its atomic mass. Therefore, the mass number equals the number of protons plus the number of neutrons.

32. The number of neutrons in the nucleus of plutonium nuclide (₉₄Pu²⁴² ) is: [66th B.P.S.C. (Pre) 2020]

Correct Answer: (b) 148
Solution:The top number (242) is the mass number (A), which represents the total number of protons and neutrons in the nucleus.

The bottom number (94) is the atomic number (Z), which represents the number of protons in the nucleus. The atomic number also defines the element.

To find the number of neutrons (N), we can use the following formula:

Substituting the values for :

33. The atoms in which the number of protons is the same, but the number of neutrons is different, are known as: [U.P.P.C.S. (Mains) 2009, Chhattisgarh P.C.S. (Pre) 2005, Uttarakhand U.D.A/L.D.A. (Pre) 2003]

Correct Answer: (d) Isotopes
Solution:The Isotopes are a set of nuclides/atoms having the same number of protons, but a different number of neutrons. In other words, the same atomic number but having different atomic mass. Each individual isotope has a separate nuclei. The Isotopes that are unstable and undergo radioactive decay are called radioisotopes.

34. Isotopes of an element differ in: [67th B.P.S.C. (Pre) 2022]

Correct Answer: (b) The mass number
Solution:The Isotopes are a set of nuclides/atoms having the same number of protons, but a different number of neutrons. In other words, the same atomic number but having different atomic mass. Each individual isotope has a separate nuclei. The Isotopes that are unstable and undergo radioactive decay are called radioisotopes.

35. Isotopes are those atoms of the same element which have: [U.P. U.D.A/L.D.A. (Pre) 2001]

Correct Answer: (b) Atomic mass is different, but the atomic number is the same.
Solution:The Isotopes are a set of nuclides/atoms having the same number of protons, but a different number of neutrons. In other words, the same atomic number but having different atomic mass. Each individual isotope has a separate nuclei. The Isotopes that are unstable and undergo radioactive decay are called radioisotopes.

36. Isotopes are that nuclei of atomic nuclei in which: [41" B.P.S.C. (Pre) 1996]

Correct Answer: (b) The number of protons is the same, but the number of neutrons is different
Solution:The Isotopes are a set of nuclides/atoms having the same number of protons, but a different number of neutrons. In other words, the same atomic number but having different atomic mass. Each individual isotope has a separate nuclei. The Isotopes that are unstable and undergo radioactive decay are called radioisotopes.

37. Radioactivity is measured by: [U.P.P.S.C. (GIC) 2010]

Correct Answer: (b) Geiger Counter
Solution:The Geiger-Muller Counter also called a Geiger Counter, is an instrument used for detection and measurement of ionizing radiation. It detects radiation such as alpha particles, beta particles and gamma rays using the ionization produced in a Geiger-Muller tube, which gives its name to the instrument

38. Radioactivity was discovered by: [U.P.P.C.S. (Mains) 2003]

Correct Answer: (b) Becquerel
Solution:Radioactivity was discovered in 1896 by the French Scientist Henri Becquerel when he was working with phosphorescent materials.

39. The isoneutronic group in the following is: [R.A.S./R.T.S. (Pre) 1999]

Correct Answer: (d) ₆C¹⁴ , ₇N¹⁵ , ₈O¹⁶
Solution:Two nuclides are iso-neutronic (isotones) if they have the same neutron number N, but a different proton number Z.

For example, Boron-12 and Carbon-13 nuclei both contain 7 neutrons and are thus isotones.

As per the question:

  • → 14−6 neutrons
  • ₇N¹⁵  → 15−7 neutrons
  • ₈O¹⁶  → 16−8 neutrons

Since the number of neutrons in all is 8, they are all isotones.