Which of the following groups of ions are always soluble in water?

The group of ions that is always soluble in water includes alkali metals and ammonium (NH4+). This is based on the solubility rules in chemistry, which dictate that all alkali metal ions (which include lithium, sodium, potassium, rubidium, cesium) and the ammonium ion are soluble in water without exception. Therefore, any compound containing these ions will dissolve completely in an aqueous solution.

In contrast, the other groups listed have specific exceptions that can affect their solubility. For instance, while carbonates and sulfates can be soluble in the presence of certain cations, there are also many carbonates and sulfates that are not soluble. Chlorides and bromides are generally soluble but can be rendered insoluble in the presence of certain metal ions, such as silver or lead. Silicates and phosphates are often insoluble, with few exceptions. Understanding these solubility trends is essential in predicting the outcome of reactions in aqueous solutions.