Which statement is always true of a weak base in water?

• A. A $1.0M$ solution of it must have $pH>12$.
• B. It has a $K{b}_{}$ value greater than $1$.
• C. It only partially reacts with water to form its conjugate acid and $O^H$.
• D. It completely dissociates in water to produce $O^H$ ions.

Answer: (C)

Verified step by step guidance

1. Understand the definition of a weak base: a weak base only partially ionizes or reacts with water, establishing an equilibrium rather than completely dissociating.
2. Recall that the base dissociation constant, \(K_b\), for a weak base is less than 1, indicating incomplete ionization in water.
3. Recognize that a weak base reacts with water to form its conjugate acid and hydroxide ions (\(\mathrm{OH}^-\)), but not all base molecules ionize.
4. Note that a strong base completely dissociates in water, producing a high concentration of \(\mathrm{OH}^-\) ions, which is not true for a weak base.
5. Conclude that the statement 'It only partially reacts with water to form its conjugate acid and \(\mathrm{OH}^-\)' is always true for a weak base in water.