Which of the following statements about flux are true?

The flux through a surface is proportional to the electric field.

When turning a surface inside of an electric field, the maximum flux is achieved if the electric field vector and the surface vector are perpendicular.

The total flux through any closed surface that does not contain a charge is zero.

The unit of flux is Vm2/C The total flux through a surface completely enclosing a charge q is q/ε

Correct --> The flux through a surface is proportional to the electric field.

The definition of the flux is the electric field passes through a given area.

Therefore, the flux is proportional to the electric field.

Wrong --> When turning a surface inside of an electric field, the maximum flux is achieved if the electric field vector and the surface vector are perpendicular.

On the contrary, the maximum flux is achieved when the electric field vector and the surface vector are parallel, since the cosine of the angle between those two vectors is at its maximum when the angle is zero.

Note that the area vector is normal to the surface.

Correct --> The total flux through any closed surface that does not contain a charge is zero.

If the closed surface does not contain any charge inside, which means that either there is no electric field present or there is an external electric field. In the first case, the flux is directly zero bu definition. In the second case, the inward flux is equal to the outward flux, so the total flux is equal to zero anyway.

Wrong --> The unit of flux is Vm2/C The total flux through a surface completely enclosing a charge q is q/ε.

The unit of flux is Vm or Nm2/C.

However, the second statement is correct. By Gauss' Law, the total flux through a surface enclosing a charge q is q/ε.