Question

Out of the following pair of elements, identify isotones:

• A. \( _1^2 H \) and \( _1^3 H \)
• B. \( _{79}^{197} {Au} \) and \( _{80}^{198} {Hg} \)
• C. \( _1^3 H \) and \( _2^3 He \)
• D. \( _{17}^{35} {Cl} \) and \( _{17}^{37} {Cl} \)
• E. \( _{92}^{235} {U} \) and \( _{92}^{238} {U} \)

Hint:

Isotones are nuclei with the same number of neutrons but different numbers of protons. To identify isotones, subtract the atomic number from the mass number and compare the result for each pair.

Answer 1

The Correct Option is B

Isotones are atoms of different elements that have the same number of neutrons but different numbers of protons. In other words, isotones have the same neutron number (\( A - Z \)) but different atomic numbers (\( Z \)).

Now, let's analyze the given options:

• Option A: \( _1^2 H \) and \( _1^3 H \)
  • These are isotopes of hydrogen, not isotones. They have the same number of protons but different numbers of neutrons.
• Option B: \( _{79}^{197} {Au} \) and \( _{80}^{198} {Hg} \)
  • These are isotones. Both have 118 neutrons (\( 197 - 79 = 118 \) and \( 198 - 80 = 118 \)), but different numbers of protons (79 for Au and 80 for Hg).
• Option C: \( _1^3 H \) and \( _2^3 He \)
  • These are not isotones. They have the same number of nucleons (3), but different numbers of protons and neutrons.
• Option D: \( _{17}^{35} {Cl} \) and \( _{17}^{37} {Cl} \)
  • These are isotopes of chlorine, not isotones. They have the same number of protons (17), but different numbers of neutrons.
• Option E: \( _{92}^{235} {U} \) and \( _{92}^{238} {U} \)
  • These are isotopes of uranium, not isotones. They have the same number of protons (92) but different numbers of neutrons.

Therefore, the correct answer is:

\[ \boxed{\text{B) } _{79}^{197} {Au} \text{ and } _{80}^{198} {Hg}} \]