The velocity components of a two dimensional plane motion of a fluid are $:u=\dfrac{y^3}{3}+2x—x^2y$ and $v=xy^2-2y-\dfrac{x^3}{3}$. The correct statement is:

1. Fluid is incompressible and flow is irrotational
2. Fluid is incompressible and flow is rotational
3. Fluid is compressible and flow is irrotational
4. Fluid is compressible and flow is rotational