The correct option is B −72
Given parabola is x2=4y and normal is x=my+c
k2+mk+m=0D=0⇒m2−4m=0⇒m=0,4
When m=0, the equation of normal becomes
x=c
This is normal only when c=0
When m=4, then equation of normal becomes
x=4y+c⋯(1)
Slope of tangent is −4
Now, differentiating the equation of parabola x2=4y
2x=4dydx⇒m=dydx=x2=−4⇒x=−8⇒y=16
Now, putting (−8,16) in equation (1), we get
c=−72