Choose the CORRECT statement that describes the dependence of the variance $\left(\sigma_{\Theta}^{2}\right)$ of the residence time distribution (RTD) with respect to the number of tanks ( $n$ ) in the Tanks-in-Series model of non-ideal reactors.
- $\sigma_{\Theta}^{2}$ monotonically increases with $n$
- $\sigma_{\Theta}^{2}$ first increases and then decreases with $n$
- $\sigma_{\Theta}^{2}$ first decreases and then increases with $n$
- $\sigma_{\Theta}^{2}$ monotonically decreases with $n$
