# Which d-block cation has the maximum hydration enthalpy?

Among $$\ce{Mn^2+}$$, $$\ce{V^2+}$$, $$\ce{Ni^2+}$$ and $$\ce{Ti^2+}$$, which cation is having the highest hydration energy to form the aqua complex $$\ce{[M(H2O)6]^2+}$$?

I guess $$\ce{Mn^2+}$$ should be the answer as it has the most stable electronic configuration.

Here, $$\ce{Ni}$$ has the smallest atomic radii compared to all other options due to greater effective nuclear charge, so it's ionic radii would also follow the same trend. Hence, $$\ce{Ni^2+}$$ would have greater hydration enthalpy.