Hardness of water is caused by the presence of

The correct option is Cations in the water.

Hardness in water is a chemical characteristic defined by the presence of dissolved multivalent metallic cations.
When water flows through soil and rock formations (such as limestone, gypsum, and chalk), it dissolves tiny amounts of minerals, primarily calcium (${\mathrm{Ca}}^{2+}$) and magnesium (${\mathrm{Mg}}^{2+}$). These positively charged ions are called cations.

While solid particles causes turbidity, pathogens cause infections, and toxic metals cause toxicity/poisoning, it is specifically these dissolved metallic cations that react with soap to form an insoluble precipitate (soap scum) and cause scale buildup in pipes and boilers, which are the defining characteristics of hard water.