The wavelength of Kα X-rays produced by an X-ray tube is 0.76 Ao. What is the atomic number of the anode material of the tube?

Kα X-rays are produced when an electron makes a transition from n=2 to n=1 to fill a vacancy in K-shell. The wavelength of X-ray lines is given by1λKα=(Z−1)2112−122⇒1λKα=34R(Z−1)2⇒(Z−1)2=43RλKα⇒(Z−1)2=43×1.097×107×0.76×10−10=1599.25⇒  Z−1=40⇒Z=41