The correct answer is: B. zeolite
Zeolite is a naturally occurring or synthetic mineral that is used as a water softener. It is a type of aluminosilicate, which means that it is made up of aluminum, silicon, and oxygen atoms. Zeolites have a honeycomb-like structure that allows them to trap and remove minerals, such as calcium and magnesium, from water. This makes water softer and less likely to cause scale buildup in pipes and appliances.
Borax is a mineral that is also used as a water softener. However, it is not as effective as zeolite and can be more difficult to use. Borax is also a potential health hazard, so it is not recommended for use in drinking water.
Option C is incorrect because both borax and zeolite are water softeners, but they are not the same thing. Borax is a mineral that is less effective than zeolite, and it can be more difficult to use. Zeolite is a naturally occurring or synthetic mineral that is more effective than borax and is easier to use.
Option D is incorrect because zeolite is a water softener.