Final answer:
The Sun is overhead in Brazil at the equator during equinoxes and at the Tropic of Capricorn during the December solstice. In Chile, only places within the Tropic of Capricorn experience the Sun directly overhead, which occurs on the December solstice.
Step-by-step explanation:
The Sun will be directly overhead in Brazil and Chile on different days, due to the tilt of the Earth's axis and its position in its orbit around the Sun. In Brazil, which extends across the equator and includes a portion of the Tropic of Capricorn, the sun is directly overhead at the equator on the equinoxes (around March 21 and September 21) and at the Tropic of Capricorn on the solstice (around December 21 or 22). However, for Chile, which lies entirely south of the equator and includes a part of the Tropic of Capricorn, the situation is similar only for places within the Tropic of Capricorn and only on December 21 or 22, when it is the summer solstice in the Southern Hemisphere.
In summary, the Sun can be overhead in Brazil at the equator on the equinoxes and at the Tropic of Capricorn on the solstice. For Chile, the Sun is overhead only in its northernmost parts, which reach the Tropic of Capricorn, on the December solstice. Locations outside these specific latitudes in Brazil and Chile will not experience the Sun being directly overhead.