If the velocity of body is doubled then % increase in centripetal force will be?
That is an increase of 300%.
Since you are asking about centripetal force, I assume you are talking about a body moving in a circular path. In that case, speed is a better term than velocity. Or even better would be "instantaneous velocity",
The formula for centripetal force,
I hope this helps,
The centripetal force
Now, the centripetal force
Now, the percent
hence the centripetal force