Major reservoir of carbon is _______

Explanation

**Step-by-Step Solution:**

1. **Understanding Carbon Reservoirs**: Carbon exists in various forms and is stored in different reservoirs on Earth. The major reservoirs include the atmosphere, oceans, terrestrial ecosystems, and geological formations.

2. **Identifying Major Reservoirs**: Among these, the oceans are known to hold a significant amount of carbon. They act as a major sink for carbon dioxide (CO2), absorbing it from the atmosphere.

3. **Carbon in Sedimentary Rocks**: In addition to the oceans, carbon is also stored in sedimentary rocks, particularly in the form of limestone. These geological formations contain large amounts of carbon that have been deposited over millions of years.

...