Question

4. All the alkali metals give characteristic flame test. The decreasing order of frequency of light emitted by the
(a) Li > Na > K > Rb > Cs
(b) Li > Na= K = Rb > Cs
(c) Cs > Rb > K > Na > Li
(d) Li = Na > K > Rb=Cs
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Answer 1

Answer:

Li>Na>K>Rb>Cs

Explanation:

The alkali metals and their salts give characteristic colour to Bunsen flame. The flame energy causesan excitation of the outermost electron which on reverting back to its initial position gives out the absorbed energy as visible light. Li-Crimson red,Na-Golden yellow, K-Pale violet, Rb and Cs-Violet.These different colours are due to different ionisation energy of alkali metals. The energy released is minimum in the case of Li and increases in the order:-

Energy released : Li < Na < K < Rb < Cs

λ: Li > Na > K > Rb > Cs

Frequency released : Li < Na < K < Rb < Cs