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Q.
The wavelength of $K_{\alpha} X$-rays for lead isotopes $Pb ^{208}, Pb ^{206}, Pb ^{204}$ are $\lambda_{1}, \lambda_{2}$ and $\lambda_{3}$ respectively.
Then
Solution:
Value of $\lambda$ here depends on atomic number.
Since $z$ is same for all species hence $\lambda_{1}=\lambda_{2}=\lambda_{3}$