Question

Which of the following pairs of ions makes the water hard?

• A. $N{a}^{+}$
  
• B. $C{s}^{+}$
  
• C. $R{b}^{+}$
  
• D. $B{a}^{+2}$

Answer 1

Answer: (A)

The correct option is A $N{a}^{+}$
Ion-exchange resin can soften both temporary and permanent hard water. The ion-exchange resin starts with sodium ions struck to it. As the bond water passes through the column, sodium ions come off the resin and go into the water.

Thus, ${Na}^{+}$ ions makes the water hard.