Moseley's equation is represented as v=a(Z−b) where, a and bare constants. If OA = 1, then atomic number of the element showing frequency of 400 Hz is

v=a(Z−b)=aZ−abThus, graph is a straight linev=0                aZ=ab                             Z=b=OA=1 Thus, b=1 and at Z=0,v=−ab             Slope =a=tan⁡45∘=1Thus               v=(Z−1)If v = 400 Hz, then                  400=Z−1    20=Z−1∴Z=21