b
\({\lambda _{{\text{K}}\alpha }} = 0.71\,{\text{Å  (}}{{\text{M}}_{\text{0}}})\,\,,\,\,\,{Z_{{M_0}}} = 42,\,\,{Z_{{C_4}}} = 29\)

\({\lambda _{K\alpha }} \propto \frac{1}{{{{(Z - 1)}^2}}}\,\)

\(\Rightarrow \,\frac{{{\lambda _{{\text{K}}{\alpha _{\text{1}}}}}}}{{{\lambda _{{\text{K}}{\alpha _{\text{2}}}}}}} = \frac{{{{({Z_2} - 1)}^2}}}{{{{({Z_1} - 1)}^2}}}\)

\(\therefore\) \({\lambda _{{K_{{\alpha _{Cu}}}}}} = \frac{{{\lambda _{{K_{{\alpha _{{K_0}}}}}}}{{({Z_{{M_0}}} - 1)}^2}}}{{{{({Z_{Cu}} - 1)}^2}}}\)

\( = \frac{{0.71 \times {{10}^{ - 10}} \times 41 \times 41}}{{{{(29 - 1)}^2}}} = \frac{{0.71 \times {{10}^{ - 10}} \times 41 \times 41}}{{28 \times 28}}\)

\(\, \Rightarrow \,\,{({\lambda _{K\alpha }})_{Cu}} = 1.52\,\,{\text{Å}}\)