Atomic Structure

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

(a) The sum of the numbers of neutrons and protons
(b) The total mass of neutrons and protons
(c) Always more than the atomic weight
(d) Always less than its atomic number
(e) None of the above/More than one of the above

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: $N = A - Z$

Substituting the values for $₉₄Pu²⁴²$ : $N = 242 - 94$

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]

(a) Isobars
(b) Isomers
(c) Isotones
(d) Isotopes

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]

(a) Atomic mass is the same, but the atomic number is different.
(b) Atomic mass is different, but the atomic number is the same.
(c) Atomic number and atomic mass are both the same.
(d) None of the above.

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]

(a) The number of neutrons is the same, but the number of protons is different
(b) The number of protons is the same, but the number of neutrons is different
(c) The number of both protons and neutrons is the same
(d) The number of both protons and neutrons is different

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]

(a) Hydrometer
(b) Geiger Counter
(c) Seismometer
(d) Ammeter

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]

(a) Rutherford
(b) Becquerel
(c) Bohr
(d) Madam Curie

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]

(a) ₆C¹² , ₇N¹⁴ , ₈O¹⁶
(b) ₆C¹² , ₇N¹⁴ , ₇N¹⁸
(c) ₆C¹⁴ , ₇N¹⁴ , ₈O¹⁶
(d) ₆C¹⁴ , ₇N¹⁵ , ₈O¹⁶

Correct Answer: (d) ₆C¹⁴ , ₇N¹⁵ , ₈O¹⁶

Solution:Two nuclides are iso-neutronic (isotones) if they have the same neutron number

, but a different proton number

.

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

As per the question:

$₆C¹⁴$ → $= 8$ neutrons
→ $= 8$ neutrons
→ $= 8$ neutrons

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

Atomic Structure

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

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

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]

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

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

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

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

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

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

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