Final answer:
Ammonium hydroxide (NH₄⁺OH) is not a strong base, unlike sodium hydroxide (NaOH), potassium hydroxide (KOH), and calcium hydroxide (Ca(OH)₂), which completely dissociate in water. The correct answer is 4) Calcium hydroxide (Ca(OH)2).
Step-by-step explanation:
Among the options given, ammonium hydroxide (NH₄⁺OH) is not a strong base. Strong bases, like sodium hydroxide (NaOH) and potassium hydroxide (KOH), completely dissociate in water to release hydroxide ions (OH⁻) and their respective cations (Na⁺ and K⁺). Ammonium hydroxide is different as it is the aqueous form of ammonia (NH₃), which is a weak base because it does not fully dissociate in water. Instead, only a small percentage of ammonia molecules react with water to form ammonium ions (NH₄⁺) and hydroxide ions (OH⁻).
Although calcium hydroxide (Ca(OH)₂) is only slightly soluble in water, the portion that does dissolve dissociates completely, making it a strong base. So, out of the given options, the answer is 4) Calcium hydroxide (Ca(OH)2).