How ion exchanger works in removing hardness of water
please help me ASAP​

Calcium (Ca2+) and magnesium (Mg2+) ions that cause water hardness can be removed fairly easily by using an ion exchange procedure. Standard water softeners are cation exchange devices. Cations refer to positively charged ions dissolved in the water. Cation exchange involves the replacement of the hardness ions with a nonhardness ion.

Water softeners usually use sodium (Na+) as the exchange ion. Sodium ions are supplied from dissolved sodium chloride salt, also called brine. In the ion exchange process, sodium ions are used to coat an exchange medium in the softener. The exchange medium can be natural “zeolites” or synthetic resin beads that resemble wet sand.

As hard water passes through a softener, the calcium and magnesium trade places with sodium ions (Figure 1). Sodium ions are held loosely and are replaced easily by calcium and magnesium ions. During this process, “free” sodium ions are released into the water.

substituting a hydrogen atom with a halogen in a hydrocarbon:

- the single bond remains single. a is wrong.

- the bond with hydrogen is as strong as with a halogen. c is wrong

- a hydrocarbon is saturated if there is no double bond. we do not know that so d is wrong.

- carbon will always have four valence electrons. e is wrong.

by elimination, the correct answer is b. the boiling point of the new compound increases.