Final answer:
The net outward electric flux through a cubical box containing two charges Q1 and Q2 is given by the sum of the charges divided by the electric constant, according to Gauss's Law.
Step-by-step explanation:
The subject of the question is Physics, more specifically, it pertains to the concept of electric flux and Gauss's Law in electrostatics. According to Gauss's Law, the net outward electric flux through any closed surface is equal to the charge enclosed divided by the electric constant (ε0).
Therefore, for a closed cubical box containing charges Q1 and Q2, the net outward flux Φ through the box is given by Φ = (Q1 + Q2) / ε0. The other provided formulas are incorrect because they do not consider the electric constant. Additionally, the formula should not include the side of the box squared (a2), as Gauss's Law does not involve dimensions of the enclosing surface.