Answer
Please see the work below.
Work Step by Step
According to thermodynamic conventions energy absorbed by a system is denoted by a positive sign, and energy released is denoted by a negative sign.
Electron affinity is defined as the energy released when an electron is added to a neutral gaseous atom. It can be either positive or negative.
Ionization energy is the energy required to remove an electron from a neutral gaseous atom. The electron removal takes place by the absorption of energy.
(a) The electron affinity of $S^{-}$.
$S^{-}_{(g)} + e^{-} → S^{2-}_{(g)} $
The electron affinity of $S^{-}$ is a negative value.
(b) The third ionization energy of titanium.
$Ti^{2+}_{(g)} → Ti^{3+}_{(g)} + e^{-} $
The ionization enthalpy value of $Ti^{2+}$ is positive.
(c) The electron affinity of $Mg^{2+}$.
$Mg^{2+}_{(g)} + e^{-} → Mg^{+}_{(g)} $
The electron affinity of $Mg^{2+}$ is a negative value.
(d) The ionization energy of $O^{2-}$.
$O^{2-}_{(g)} → O^{-}_{(g)} + e^{-} $
The ionization enthalpy value of $O^{2-}$ is positive.
