**Core Concept**
Potassium channel openers are a class of drugs that activate certain potassium channels, leading to an increase in potassium efflux from cells. This results in hyperpolarization of the cell membrane, which can have various therapeutic effects such as vasodilation and anti-arrhythmic properties.

**Why the Correct Answer is Right**
Potassium channel openers, such as minoxidil and diazoxide, work by binding to and activating ATP-sensitive potassium channels (K_ATP channels). This activation leads to an increase in potassium ion flow out of the cell, resulting in hyperpolarization of the cell membrane. This effect is particularly beneficial in the treatment of hypertension and certain types of arrhythmias.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not a potassium channel opener.
**Option B:** This option is not a potassium channel opener; it is actually a beta-blocker used to treat hypertension and angina.
**Option C:** This option is not a potassium channel opener; it is actually a calcium channel blocker used to treat hypertension and angina.

**Clinical Pearl / High-Yield Fact**
Potassium channel openers can cause significant vasodilation, which can lead to hypotension as a side effect. This is particularly important to consider in patients with pre-existing hypotension or those taking other medications that lower blood pressure.

**Correct Answer:** C. Diazoxide is a classic potassium channel opener used to treat severe hypertension.