Gauss's Law states that the total electric flux \( \Phi_E \) through a closed surface is directly proportional to the charge enclosed within the surface. Mathematically, it is expressed as:
\[
\Phi_E = \frac{q}{\epsilon_0}
\]
where:
- \( \Phi_E \) is the total electric flux,
- \( q \) is the charge enclosed by the surface,
- \( \epsilon_0 \) is the permittivity of free space.
The product of the total electric flux and the permittivity of free space is given by:
\[
\Phi_E \times \epsilon_0 = \frac{q}{\epsilon_0} \times \epsilon_0 = q
\]
Thus, the correct answer is \( \frac{q}{\epsilon_0} \).
Therefore, the correct answer is option (B), \( \frac{q}{\epsilon_0} \).