Q1: The critical exist gradient of seepage water in soils, is

ANS:E - none of these.

Exit gradient depends upon head loss and seepage length

The total head loss H between the last two equipotential lines is 0.62 m. The distance between the two equipotential lines on the downstream end in the X area is 3.3 m.

The exit gradient is then computed as 0.62 divided by 3.3 making the upward gradient 0.19. The critical exit gradient differs from the critical hydraulic gradient.

Critical exit gradient is the ratio of seepage head loss to the length of seepage it means it not related to specific gravity or voids ratio.

It is directly proportional to head loss and inverse to the length of seepage.
  Value of critical exit gradient is 1. So it doesn't depend on any factor. Hydraulic gradient depends on Specific gravity and void ratio. Seepage velocity = velocity gradient/porosity.