Final answer:
The formula for diiodine pentasulfide, indicated by the prefixes 'di-' for two iodine atoms and 'penta-' for five sulfur atoms, is I2S5.
Step-by-step explanation:
The formula for diiodine pentasulfide is derived by looking at the prefixes and the elements involved. The prefix "di-" indicates that there are two iodine atoms, and "penta-" indicates that there are five sulfur atoms. Therefore, the correct formula is I2S5. This compound consists of two iodine (I) atoms and five sulfur (S) atoms, making the formula I2S5.