Explanation

(d)
During the softening process the reaction takes place as :
$Na_{2}Ze + Ca\ \left( HCO_{3} \right)_{2}\ \rightarrow CaZe + 2NaHCO_{3}$
$Na_{2}Ze + Mg\left( HCO_{3} \right)_{2}\ \rightarrow MgZe + 2NaHCO_{3}$
After sometime, the zeolite is completely converted into calcium and magnesium zeolites. Eventually, the bed ceases to soften water i.e., it gets exhausted. At this stage, the supply of hard water is stopped and the exhausted zeolite is reclaimed by treating the bed with a 10% NaCl solution (Brine soln.) when the following reaction takes place
$CaZe\ or\ Mgze + 2NaCl\ \ \rightarrow Na_{2}Ze\ \ \ \ \ \ \ \ \ + CaCl_{2}\ or\ MgCl_{2}$
Reclaimed zeolite