The frequency of the K_ characteristic X-ray line emitted by an element with atomic number Z=41 is f . The frequency of the K_ line emitted by an element with atomic number Z=21 will be:

Step-by-step solution

According to Moseley's Law, the frequency of the characteristic X-ray is related to the atomic number Z as: = a(Z - b) For K_ lines, the screening constant b 1 . For the first element ( Z₁ = 41 ): f (41 - 1) = 40 For the second element ( Z₂ = 21 ): f' (21 - 1) = 20 Taking the ratio of the two equations: f' f = 20 40 = 1 2 Squaring both sides: f' f = 1 4 f' = f 4 Answer: f 4