Question:
Which of the following statements is correct about isotopes of hydrogen?
Which of the following statements is correct about isotopes of hydrogen?
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Isotopes have identical electronic structure, so bond lengths remain almost unchanged.
Updated On: Jul 18, 2026
- Internuclear distance in hydrogen and deuterium is same
- Enthalpy of bond dissociation of deuterium is less than hydrogen
- Order of relative abundance of isotopes is H > T > D
- Ratio of neutrons to protons is greater for D than T
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The Correct Option is A
Solution and Explanation
Step 1: Understand isotopes of hydrogen.
Hydrogen has three isotopes: protium (H), deuterium (D), and tritium (T). They differ only in neutron number, not in electronic configuration, so chemical bonding behavior is similar but with small isotopic effects.
Step 2: Internuclear distance concept.
Bond length in diatomic molecules like $H_2$ and $D_2$ depends mainly on electronic distribution. Since isotopes have identical electronic structures, the internuclear distance is essentially the same. Thus statement (1) is correct.
Step 3: Bond dissociation enthalpy comparison.
Due to isotopic effect, $D_2$ has slightly higher bond dissociation enthalpy than $H_2$ because heavier nuclei reduce vibrational zero-point energy. Hence statement (2) is incorrect.
Step 4: Relative abundance of isotopes.
Natural abundance follows: \[ H \gt D \gt T \] Tritium is radioactive and extremely rare. Therefore statement (3) is incorrect.
Step 5: Neutron-to-proton ratio analysis.
For D: neutrons/protons = 1/1 = 1 For T: neutrons/protons = 2/1 = 2 Thus ratio is greater for T, not D. Hence statement (4) is incorrect.
Step 6: Final conclusion.
Only statement (1) is correct: \[ \boxed{\text{Option (1)}} \]
Hydrogen has three isotopes: protium (H), deuterium (D), and tritium (T). They differ only in neutron number, not in electronic configuration, so chemical bonding behavior is similar but with small isotopic effects.
Step 2: Internuclear distance concept.
Bond length in diatomic molecules like $H_2$ and $D_2$ depends mainly on electronic distribution. Since isotopes have identical electronic structures, the internuclear distance is essentially the same. Thus statement (1) is correct.
Step 3: Bond dissociation enthalpy comparison.
Due to isotopic effect, $D_2$ has slightly higher bond dissociation enthalpy than $H_2$ because heavier nuclei reduce vibrational zero-point energy. Hence statement (2) is incorrect.
Step 4: Relative abundance of isotopes.
Natural abundance follows: \[ H \gt D \gt T \] Tritium is radioactive and extremely rare. Therefore statement (3) is incorrect.
Step 5: Neutron-to-proton ratio analysis.
For D: neutrons/protons = 1/1 = 1 For T: neutrons/protons = 2/1 = 2 Thus ratio is greater for T, not D. Hence statement (4) is incorrect.
Step 6: Final conclusion.
Only statement (1) is correct: \[ \boxed{\text{Option (1)}} \]
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