Q.

Kα wavelength emitted by an atom of atomic number Z = 11 is λ. Find the atomic number for an atom that emits Kα radiation with wavelength 4λ.                [2005]

1 Z = 6  
2 Z = 4  
3 Z = 11  
4 Z = 44  

Ans.

(1)

For Kα,  1λ∝(Z-1)2

∴  λ2λ1=(Z1-1)2(Z2-1)2⇒4λλ=(11-1)2(Z2-1)2

⇒Z2-1=102

∴  Z2=6