Suppose a gaseous mixture of He,Ne,Ar and Kr is irradiated with photons of the frequency appropriate to ionize Ar,What ion(s) will be present in the mixture?
- Ar+
- Kr+
- He+
- Both A and B
The Correct Option is B
Solution and Explanation
The correct answer is option (B): Kr+
Explanation:
When a gaseous mixture of He, Ne, Ar, and Kr is irradiated with photons that have just enough energy to ionize argon (Ar), the following points are important:
- Ionization energy is the energy required to remove an electron from an atom.
- If a photon has energy equal to the ionization energy of Ar, then it has enough energy to ionize atoms with lower ionization energy than Ar, but not those with higher ionization energy.
Ionization energies (approximate values):
- He: 24.6 eV
- Ne: 21.6 eV
- Ar: 15.8 eV
- Kr: 14.0 eV
Since the photon energy is just enough to ionize Ar (15.8 eV), it cannot ionize He or Ne (which require more energy), but it can ionize Kr (which requires less).
Hence, only Kr will be ionized, forming Kr+.
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