The correct option is A (x−a)y2=x3
Let mid point of the chord is p(h,k)
Thus its equation is given by, T=S1
⇒hx−ky=h2−k2⇒y=hkx+k2−h2k
Given this line is tangent to the parabola y2=4ax
Thus Using condition of tangency, c=am
⇒k2−h2k=akh⇒(h−a)k2=h3
Hence required locus is, (x−a)y2=x3