The correct option is C 4a
We have, (x−2a)2+y2=x2
⇒x2−4ax+4a2+y2=x2
⇒y2=4ax−4a2=4a(x−a)
Comparing it with standard parabola Y2=4bX
Y=y,X=x−a,b=a
We know length of latus rectum of parabola Y2=4bX is 4b
Hence length of latus rectum of given parabola is =4×a=4a