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Atoms — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsAtoms1 Mark
MCQ
For question two statements are given$-$one labelled Assertion $(A)$ and the other labelled Reason $(R).$ Select the correct answer to these questions from the codes $(a), (b), (c)$ and $(d)$ as given below.
Assertion $(A):$ Balmer series lies in the visible region of electromagnetic spectrum.
Reason $(R): \frac{1}{\lambda}=\text{R}\Big(\frac{1}{2^2}-\frac{1}{\text{K}^2}\Big)$, where $K = 3, 4, 5, ...$
  • A
    Both $A$ and $R$ are true and $R$ is the correct explanation of $A.$
  • ✓
    Both $A$ and $R$ are true but $R$ is not the correct explanation of $A.$
  • C
    $A$ is true but $R$ is false.
  • D
    $A$ is false and $R$ is also false.
✓

Answer

Correct option: B.
Both $A$ and $R$ are true but $R$ is not the correct explanation of $A.$
When we put $R = 10^7m^{-1}$ and $K = 3, 4 5,$ in the given formula, values of $\lambda$ calculated lie between $4000A$ and $8000A,$ which is the visible region. The reason is true, but does not explain the assertion properly.

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