Which of the following is not a freshwater resource?

Ocean

The correct answer is option 3. Ocean.

The ocean is not considered a freshwater resource because it contains saltwater, which is not suitable for most human uses without desalination. The water in oceans is composed of a significant amount of dissolved salts, mainly sodium chloride, along with other minerals.

On the other hand:

1. Rivers: Rivers primarily contain freshwater, which comes from precipitation (rain and snow) and is generally suitable for various human and ecological needs.

2. Groundwater: Groundwater is another source of freshwater found beneath the Earth's surface in aquifers. It accumulates as a result of the infiltration of rainwater and is often used for drinking water and irrigation.

While rivers and groundwater are sources of freshwater, the ocean's water is saline. Desalination technologies can be employed to make seawater potable, but the process is energy-intensive and not as widely implemented on a large scale compared to using naturally occurring freshwater sources.