Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.

### Instruction:
Determine the 4th special element given the following 4 elements.

### Input:
Iron, Nickel, Lead, Mercury

### Response:
Sulfur. Iron, Nickel, Lead, and Mercury make up the four basic components of gunpowder, while Sulfur is the fourth special element that reacts with the other components to cause an explosion.