c
The amount of energy required to remove an electron from unipositive ion is referred as second İonisation potential.

In \(Ti, V, Cr\) and \(Mn\), generally second ionisation energy increases with increase in atomic number but second ionisation potential of \(Cr\) is greater than

that of \(Mn\) due to the presence of exactly half-filled \(d-\)subshell in \(Cr\). Thus, the order of second ionisation enthalpy is

\(\mathrm{Cr}>\mathrm{Mn}>\mathrm{V}>\mathrm{Ti}\)