What explains the eastward flow of the equatorial counter-current?

The correct option is Convergence of the two equatorial currents.

To understand why this happens, we can look at the dynamics of surface ocean currents near the equator:
1. The Trade Winds (North-East Trades and South-East Trades) blow westward across the tropical oceans in both hemispheres.
2. These winds drive two major ocean currents westward: the North Equatorial Current and the South Equatorial Current.
3. As these two massive currents move westward, they pile up huge volumes of water on the western side of the ocean basins (such as the western Pacific and western Atlantic oceans).
4. Because water is converging and accumulating on the western side, it creates a hydraulic gradient—literally a slight slope where the sea level is higher in the west than in the east.
5. Due to gravity, this piled-up water seeks to flow back down the gradient toward the east. It finds a path of least resistance in the Intertropical Convergence Zone (ITCZ), a belt of light and variable winds near the equator where the wind stress pushing westward is weakest.
6. This return flow, driven by the convergence and piling up of water from the two equatorial currents, travels eastward between them and is known as the Equatorial Counter-Current.