Question

Choose the pair of isotones from the following.

(A) ₈O¹⁷& ₈O¹⁶

(B) ₁₂ Mg²⁴&₁₁Na²⁴

(C)₁₈Ar⁴⁰ &₁₉K⁴⁰

(D)₁₁Na²³&₁₂Mg²⁴

• A. A
• B. B
• C. C
• D. D

Answer 1

Answer:

D. D

• Isotones are nuclides (atoms of different elements or isotopes of the same element) that have the same number of neutrons but different atomic numbers (number of protons).

• Mathematically, if N represents the number of neutrons, then for two isotones, N1 = N2.

• The number of neutrons (N) in a nuclide can be calculated as: N = A - Z, where A is the mass number and Z is the atomic number.

Analyzing the Options:

• Option (A): ₈O¹⁷ & ₈O¹⁶

  • For ₈O¹⁷: Atomic Number (Z) = 8, Mass Number (A) = 17. Neutrons (N) = 17 - 8 = 9.

  • For ₈O¹⁶: Atomic Number (Z) = 8, Mass Number (A) = 16. Neutrons (N) = 16 - 8 = 8.

  • Since the number of neutrons is different (9 vs 8), these are not isotones. They are isotopes of Oxygen (same Z, different A).

• Option (B): ₁₂ Mg²⁴ & ₁₁Na²⁴

  • For ₁₂ Mg²⁴: Z = 12, A = 24. N = 24 - 12 = 12.

  • For ₁₁Na²⁴: Z = 11, A = 24. N = 24 - 11 = 13.

  • Number of neutrons are different (12 vs 13). These are isobars (same A, different Z).

• Option (C): ₁₈Ar⁴⁰ & ₁₉K⁴⁰

  • For ₁₈Ar⁴⁰: Z = 18, A = 40. N = 40 - 18 = 22.

  • For ₁₉K⁴⁰: Z = 19, A = 40. N = 40 - 19 = 21.

  • Number of neutrons are different (22 vs 21). These are isobars (same A, different Z).

• Option (D): ₁₁Na²³ & ₁₂Mg²⁴

  • For ₁₁Na²³: Atomic Number (Z) = 11, Mass Number (A) = 23. Neutrons (N) = 23 - 11 = 12.

  • For ₁₂Mg²⁴: Atomic Number (Z) = 12, Mass Number (A) = 24. Neutrons (N) = 24 - 12 = 12.

  • The number of neutrons is the same (12) for both nuclides, while their atomic numbers are different (11 and 12). Therefore, these are isotones.