Statement I: In a transistor, the base is made thin.
Statement II: A thin base makes the transistor stable.

detailed solution

Correct option is B

In a transistor the base is lightly doped and very thin. This feature is main concept of transistor action on account of which only few holes (less than 5%) combine with the electrons in base region. Thickness of base region is so small that most of electrons diffusing through base region cross over through collector region. By reducing the base width, the power of transistor increases but it does not mean that transistor becomes stable.