The differential equation of all parabola whose axis of symmetry is parallel to x-axis is of order

3

The correct answer is option (2) : 3

The general equation of all parabola whose axis of symmetry is parallel to x axis is

$x= ay^2 + by + c, $ where a, b , c are arbitrary constants.

As there are there arbitrary constants.

So the required differential equation is of order 3.