____________ does not exist in solid state.
Correct option explanation:
(A) Hydration enthalpy (ꕔHHyd) is the change in enthalpy when one mole of gaseous ion under a standard condition of 1 bar pressure dissolves in a sufficient amount of water to form an infinitely dilute solution.
containing cations has the highest hydration enthalpy, So, it does not exist in solid-state.
Incorrect option explanation:
Options (B), (C), and (D) are having generally low hydration enthalpy and can exist in solid-state.
Thus, due to the high hydration enthalpy, option (A) is the correct option.