During the course of the day, which location had the greatest intensity of insolation at solar noon?
(1) a
(2) b
(3) c
(4) d

The correct answer is - (3) C.

The location C will have the greatest intensity of insolation at solar noon because the Sun will appear right above the location at noon, thus the sun radiation will fall at an angle of 90°.

It is very simple to determine where the solar insolation will be the highest, if the sun is higher on the sky, than the insolation is bigger as the Sun's radiation falls at an angle to allows for more direct insolation, while if the Sun is lower on the horizon, than the insolation will be lower because the Sun's radiation falls at a sharper angle ans is more dispersed.

The location C is a location that is in the Equator, or very close to the Equator, as those are the only places on the planet where the Sun appears at noon right above a certain place, or rather an angle of 90°