एक वर्णी प्रकाश का एक पुंज \(Li ^{++}\)आयन के इलेक्ट्रॉन को प्रथम कक्ष से तृतीय कक्ष में उत्तेजित करने में प्रयुक्त किया जाता है। एकवर्णी प्रकाश की तरंगदैर्ध्य \(x \times 10^{-10} m\) प्राप्त होती है। \(x\) का मान ज्ञात कीजिए। [दिया है: \(hc =1242 eV\) \(nm ]\)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.