Electric flux \( \varphi \) has the dimension of charge, and from the equation \( \varphi = \alpha \lambda + \beta \sigma \), the dimensions of \( \alpha \) and \( \beta \) can be found by equating the dimensions of each term. The dimensions of \( \lambda \) (linear charge density) are \( M L^{-1} T^{-1} \) and of \( \sigma \) (surface charge density) are \( M L^{-2} T^{-1} \).
After solving for \( \frac{\beta}{\alpha} \), we find the dimensions are \( M L^3 T^{-2} \).
Thus, the correct answer is option (2).