How instantaneous velocity can be found by graphical method ?

Mark the wrong statement :-

For the displacement-time graph shown in figure, the ratio of the magnitudes of the (constant) speeds during the first two seconds and the next four seconds is

Which of the following options is correct for the object having a straight line motion represented by the following graph

A particle located at $x= 0$ at time $ t= 0 $, starts moving along with the positive $x-$direction with a velocity $v$ that varies as $v$ $=$ $\alpha \sqrt x $. The displacement of the particle varies with time as