On 21st June, the Sun

Answer: (a) does not set below the horizon at the Arctic Circle

It is the northern summer solstice: 24 hours of daylight at the Arctic Circle.

The idea

Earth’s axis remains pointed nearly in the same direction as Earth moves around the Sun. This makes the latitude of the overhead noon Sun shift north and south during the year. When it reaches its northern limit, the northern polar region has its longest daylight period.

Earth revolves around the Sun → Its axis keeps nearly the same direction → Northern hemisphere leans towards the Sun in June → Overhead noon Sun reaches its northern limit → Northern polar region remains sunlit through the rotation

Why the others are wrong

(b) On 21 June the ANTARCTIC Circle has 24 hours of night.

(c) The Sun is overhead at the equator only at the equinoxes (about 21 March and 23 September).

(d) The Sun is overhead at the Tropic of Capricorn on about 22 December.

The trap

(b) is the same sentence with the other pole. On 21 June the south polar circle is in total darkness.

Elimination technique

At the June solstice the overhead Sun is at its northern limit. That rules out both overhead-Sun options; the southern polar region is in winter, which removes (b).

Also know

An equinox places the overhead noon Sun at the equator; a solstice places it at a tropic. Outside the tropics the Sun is never directly overhead. Solstice dates can vary slightly from year to year, so 21 June is the usual textbook date rather than an unchanging calendar rule.