The figure shows different graphs in case of a thin convex lens for the formation of a real image, u and v are the object and image distances respectively. Find out the correct identification for the different combinations from the following.

when real image is formed by a convex lens then lens equation will be  1u+1v=1f ∴vu+1=vf∴1y+1=xf  graph cannot be a straight line∴  Option (1) is not correct. Graph II has increase in u increase v which is not correct.Eq. vu+1=vf  gives  1+y=xf∴  Linear graph (III) is not correct∴ 1u+1v=1f   gives graph IV, Hence, option (4) is correct.