Which one is the principal cation in the plasma of blood ?

The concentration of $N{a}^{+}$ in plasma is 0.32% fllowed by $K^{+}\left(0.02\%\right)$ and magnesium (0.0025%).
The minerals iron like $N{a}^{+}$ and others present in the blood plasma play an essential role in the maintenance of osmotic pressure of blood.