A vessel containing water is given a constant accelerationtowards the right, along a straight horizontal path. Which of the following diagrams represents the surface of the liquid?
(A).

(B).

(C).

(D).

Hint: As the vessel is accelerating, there is net force acting on it. Similarly there must be some forces acting on the water in the vessel. The final motion of the water will be decided by direction of net force acting on it. Since water has no motion, there is some inertia acting in it.

Complete answer:
Water or all other fluids are shapeless and take up the shape of the container in which they are kept.
When the vessel is accelerated towards the right, water inside it will also experience a force due to motion of the vessel. The other forces acting on the water are gravitational forces due to Earth and inertial forces also called pseudo forces.
Pseudo forces will act on water because water has mass and hence, it will also have inertia.

As in the above figure, by the parallelogram law of vector addition, the resultant of the forces acting on the water in the vessel is towards the left. This means the all forces will push it towards the left, opposite to the motion of the vessel. The correct diagram that will depict this case is-

Therefore, the correct option is (C).

Note:
Inertia is the tendency of a body to oppose the change in its state of rest or motion. Inertia is directly proportional to the mass. In the above case, inertia causes pseudo forces to act on water. As the vessel is accelerating, according to Newton’s second law of motion, there is net force acting on it.