Which of the following is NOT a strong base?

The correct choice indicates that magnesium hydroxide, Mg(OH)2, is not considered a strong base in the same way as the other options listed. Strong bases are typically substances that completely dissociate in water to release hydroxide ions (OH-).

Potassium hydroxide (KOH), sodium hydroxide (NaOH), and lithium hydroxide (LiOH) are all strong bases because they dissociate completely in aqueous solution, providing a high concentration of hydroxide ions.

On the other hand, magnesium hydroxide is classified as a sparingly soluble hydroxide, meaning that while it does dissociate, it does not do so to the same extent as the others. This results in a low concentration of hydroxide ions in solution, thus not behaving as a strong base under standard conditions. Its limited solubility means that even when it does dissociate, it does not produce a high enough concentration of hydroxide ions to be classified as a strong base like the others listed.