The pressure in a liquid at two points in the same horizontal plane are equal.Consider an elevator accelerating upward and a car accelerating on a horizontal road.The above statement is only correct in

a. The car only.

b. The elevator only

c. Both of them

d . Neither of them

This is valid in the elevator only.

In  the car ,a pseudo force is acting on the water in the direction opposite to that of the acceleration.

As such there is a difference of lpa(l is the horizontal distance between two points , p is the density oif fluid , a is the aceleration of the car) in pressure even in points in horizinatal planes.

This is not the case of elevator , as in case of elevator , the pseudo force is acting downwards and as such pressure will increase but by equal amounts in all the points in horizonatal plane. As such there is no difference in the pressure b/w the two points in horizontal plane   

correct only for elevator.

in car even in x direction pseudo force acts due to acceleration

resulting in elevation of one side of water.

hene ,pressure wil be same only at an angle tan inverse (a/g) with de horizontal