Final answer:
Graphite as a coolant in nuclear reactors has the disadvantage of being prone to fire and combustion, but does not include corrosion resistance or low cost of production as disadvantages.
Step-by-step explanation:
The disadvantages of using graphite as a coolant in a nuclear reactor, particularly highlighted by the Chernobyl disaster, do not include corrosion resistance or low cost of production. These are potential advantages. Instead, the primary disadvantage is that graphite is prone to fire and combustion (Option C), which can lead to catastrophic safety incidents. High efficiency in heat transfer is typically seen as an advantage, not a disadvantage. It's important to note that water is the most commonly used reactor coolant in the United States due to its relative safety and efficiency.