Which of the following is an example of a strong base?

The correct answer is NaOH, which is a strong base. A strong base is defined as a substance that completely dissociates into its ions in an aqueous solution. When NaOH is dissolved in water, it dissociates fully into sodium ions (Na⁺) and hydroxide ions (OH⁻). The presence of a high concentration of hydroxide ions in solution is what gives strong bases their characteristic of raising the pH significantly.

In contrast, other options represent different types of substances. NH4Cl is an ammonium salt that, when dissolved in water, produces NH4⁺, which can release protons (H⁺) and act as a weak acid. H2SO4 and HCl are strong acids; both dissociate completely in water to yield H⁺ ions and their respective anions, leading to a drop in pH rather than an increase. Thus, NaOH stands out as the example of a strong base due to its ability to create a high concentration of hydroxide ions in solution.