. . . . . . . . is used to suppress unwanted conduction. A. Phosphorus B. Boron C. Silicon D. Oxygen

The correct answer is B. Boron.

Boron is used to suppress unwanted conduction in semiconductors. It is a p-type dopant, which means that it adds holes to the semiconductor material. Holes are positively charged particles that can move through the material, and they can interfere with the flow of electrons. By adding boron to a semiconductor, the number of holes is increased, which makes it more difficult for electrons to flow. This can be used to control the conductivity of the material, and it is a common technique in semiconductor manufacturing.

The other options are incorrect for the following reasons:

• A. Phosphorus is an n-type dopant, which means that it adds electrons to the semiconductor material. Electrons are negatively charged particles that can move through the material, and they can increase the flow of current. This is the opposite of what is desired in order to suppress unwanted conduction.
• C. Silicon is the main component of most semiconductors. It is a pure semiconductor, meaning that it does not have any dopants added to it. As such, it does not have any effect on the conductivity of the material.
• D. Oxygen is a common impurity in semiconductors. It can act as a donor or an acceptor dopant, depending on the type of semiconductor material. In either case, it will affect the conductivity of the material, but it will not suppress unwanted conduction.