Which statement describes a dilute base?

• A. It contains a small number of OH- ions.
• B. It contains a large number of OH- ions.
• C. It completely ionises in solution.
• D. It does not ionise in solution.

Answer: (A)

Bases in water produce hydroxide ions (OH−). If the base is dilute, there are only a small amount of that OH− in the solution, so the solution has a low concentration of hydroxide ions. This is what the statement about a dilute base describes best. The other ideas describe either having a lot of OH− (a concentrated base), or how completely the base ionises (which relates to strength, not how dilute it is), or not ionising at all (not typical for bases in water).