(i) The decreasing order of hydration enthalpy is −Be2+ > Mg2+ > Ca2+ > Sr2+ > Ba2+
(ii) A suspension of magnesium hydroxide in water is called milk of magnesia. It is used as antacid in medicine.
(iii) Significance of Mg and Ca in biological fluids
(a) All enzymes that utilize ATP in phosphate transfer require magnesium as the cofactor.
(b) The main pigment is chlorophyll which contains magnesium.
(c) About 99% of body calcium is present in bones and teeth which is essential for them.
(d) Ca plays and important role in neuromuscular function, interneuron transmission, cell membrane integrity and blood coagulation.