What latitude receives the highest angle of insolation on march 21?

On March 21, which is the spring equinox, the latitude that receives the highest angle of insolation is the equator (0 degrees latitude). During this time, the sun is directly overhead at the equator, leading to the most direct sunlight and maximum insolation. Locations at higher latitudes receive sunlight at a lower angle, resulting in less intense insolation.