Does the number of ions in solution increase, decrease, or remain constant?

It continuously decreases.

It continuously increases.

It decreases at first, then increases.

It increases at first, then decreases.

The correct option is "C."  It decreases at first, then increases.

Explanation:

Considering the example below, which wish to prove what happens to the ions when they react in solutions:

The question is,  How does this evidence indicate that the reaction has occurred between ions?

By adding H2SO4 to Ba(OH)2 you are producing BaSO4, a mostly insoluble compound. As you increase the volume, and thereby the concentration of SO4-2 ions, you will see a precipitate form. This means that the [Ba+2] will decrease, the [H+] will increase with each addition of H2SO4, the [OH-] will react with the [H+] making H2O the same and the [SO4-2] will decrease because it reacts with the [Ba+2]. The more precipitate formed, the fewer Ba+2 and SO4-2 ions will be in solution and the fewer [H+] and [OH-] until the current is near 0 mA, then you will have excess of SO4-2 and H+ the number of ions increase again increasing the conductivity