Among the following, the solution which shows the lowest osmotic pressure is

$$\begin{gathered} \pi =C_{effective}RT \\ 1.C_{effective}=0.1\times 2=0.2M \\ 2.C_{effective}=0.05\times 3=0.15M \\ 3.C_{effective}=0.04\times 4=0.16M \\ 4.C_{effective}=0.03\times 4=0.12M \\ {K}_3\left[Fe{\left(CN\right)}_6\right]=3K^{\oplus }+{\left[Fe{\left(CN\right)}_6\right]}^{3-} \\ {C}_{effective}\text{\hspace{0.17em} is lowest for 4.} \end{gathered}$$