CSIR NET June 2016 Q118: Meteorology
The zone of highest mean annual temperature (the 'heat equator') reflects both maximum year-round solar insolation near the geographic equator and the stronger, more rapid heating of land relative to ocean (continentality effect).
Land surfaces heat up more intensely than oceans for the same solar input (lower heat capacity, no evaporative cooling/mixing), so the warmest mean annual temperatures occur over continental areas at low latitudes, and since insolation is most consistently high at the equator itself, the combination of equatorial insolation and continentality places the zone of highest average annual temperature at the equator over land. Option 1 is correct.
1) Correct -- combines maximum equatorial insolation with the stronger heating of land relative to ocean/tropics of the summer hemisphere. 2) Incorrect -- oceans, due to their high heat capacity and evaporative cooling, do not reach the extreme temperatures land does. 3) and 4) Incorrect -- these describe reasonable but secondary considerations (pure equatorial location or ocean proximity) that do not by themselves capture the dominant land-heating effect.