A cobalt (atomic no. =27 ) target is bombereded with electrons and the wavelength of its characteristic `x`-rays spectrum are measured. A second weak characteristic spectrum is also found due to an impurity in the target. The wavelength of the `K_(alpha)` lines `225.0pm` (cobalt ) and `100.0pm` (impurity). Atomic number of the impurity is `(take b=1)`

Options

A. 39
B. 40
C. 59
D. 60

Answer

B

Explanation

Using Mosely's law for both cobaly and impurity
`sqrt(f)=K(Z-1)rArr sqrt((c)/(lamda))=K(Z-1)`
`rArr sqrt((c)/(lamda_(co)))=K(Z_(infty)-1)`
and `sqrt((c)/(lamda_(x)))=K(Z_(x)-1)`
`rArr sqrt((lamda_(co))/(lamda_(x)))=(Z_(x)-1)/(Z_(co)-1)=Z_(x)=40`