Which of the following is a weak base in water?

• A. $KOH$ (potassium hydroxide)
• B. $NaOH$ (sodium hydroxide)
• C. $N_{2}H4$ (hydrazine)
• D. $Ca\left(OH\right)2$ (calcium hydroxide)

Answer: (C)

Verified step by step guidance

1. Identify the nature of each compound in water by considering their dissociation and strength as bases. Potassium hydroxide (KOH), sodium hydroxide (NaOH), and calcium hydroxide (Ca(OH)₂) are all metal hydroxides known to be strong bases because they dissociate completely in water.
2. Understand that a strong base completely ionizes in aqueous solution, producing hydroxide ions (OH⁻) readily, which results in a high pH and strong basicity.
3. Recognize that hydrazine (N₂H₄) is a molecular compound that does not fully ionize in water. Instead, it acts as a weak base by accepting protons partially, which means it produces fewer hydroxide ions compared to strong bases.
4. Recall that weak bases only partially ionize in water, establishing an equilibrium between the base and its conjugate acid, which can be represented by the equilibrium expression: \(\mathrm{B + H_2O \rightleftharpoons BH^+ + OH^-}\).
5. Conclude that among the given options, hydrazine (N₂H₄) is the weak base because it does not fully dissociate in water, unlike the metal hydroxides which are strong bases.