Final answer:
Gauss's law for electricity yields electric flux directly. Therefore, the correct option is A.
Step-by-step explanation:
The equation that yields electric flux directly is Gauss's law for electricity.
Gauss's law for electricity states that the electric flux through any closed surface is equal to the electric charge enclosed by the surface. This law relates the electric field to the electric charge it produces.
For example, if we have a spherical surface enclosing a positive charge, the electric flux through the surface is directly proportional to the charge enclosed.