Explanation:

- INSAT/GSAT satellites are mainly used for telecommunication, broadcasting, and meteorological services in India.

- These satellites commonly use the C band (around 4–8 GHz) and Ku band (around 12–18 GHz) for their communication payloads.

- The Ka band (around 26–40 GHz) is starting to be adopted in newer satellite systems, but it’s not widely used so far in the INSAT/GSAT series' main operations.

- MF (Medium Frequency) refers to 300 kHz–3 MHz and is mainly used for AM radio, maritime, and navigation—not for satellite communications at all.

Option 3: MF is the correct answer.

MF is not used in INSAT/GSAT satellite communication. The other bands (C and Ku) are commonly used, and Ka is emerging.