Hardness of water is due to presence of salts of :

Options

1. A$\mathrm{Na}^{+}$and $\mathrm{K}^{+}$
2. B$\mathrm{Ca}^{2+}$ and $\mathrm{Mg}^{2+}$
3. C$\mathrm{Ca}^{2+}$ and $\mathrm{K}^{+}$
4. D$\mathrm{Ca}^{2+}$ and $\mathrm{Na}^{+}$