Final answer:
The smallest current that can be fatal under certain conditions is a microcurrent. A current as small as 20.0 µA can cause ventricular fibrillation if applied directly to the heart, and special electrical safety precautions are needed in such cases.
Step-by-step explanation:
The smallest current that can be fatal under certain conditions is microcurrent (a). For instance, during surgery, a current as small as 20.0 µA applied directly to the heart may lead to ventricular fibrillation, a life-threatening condition. It's critical to understand that currents around 0.06 A can also be potentially fatal, making the heart fibrillate in an uncontrolled manner. Even currents less than 5 mA, under certain conditions, can cause a dangerous shock if they pass through the body under the right conditions, such as wet skin reducing the body's resistance.
Thus, even a very small voltage can become dangerous if the resistance of the body or the path through the body is low enough. For example, applying ohm's law (I = V/R), you'll find that a voltage as low as that resulting from the 20.0 µA current through a 300 Ω resistance (the exposed heart during surgery) warrants careful consideration of electrical safety precautions to avoid such a fatal outcome.