Exp) Option b is the correct answer.

In the northern hemisphere, the longest day of the year is called the summer solstice.

The maximum amount of sunlight received by the Northern Hemisphere during this time is usually on June 20, 21 or 22.

The longest day of 2021 for those living north of the Equator is June 21. This day is referred to as the summer solstice, the longest day of the summer season. It occurs when the sun is directly over the Tropic of Cancer, or more specifically right over 23.5 degree north latitude.

Source: https://indianexpress.com/article/explained/summer-solstice-explained-why-june-21-will-be-the-longest-day-of-the-year-in-northern-hemisphere-7367636/#:~:text=in%20Northern%20Hemisphere-,Summer%20solstice%3A%20Why%20June%2021%20will%20be%20the%20longest%20day,the%20year%20in%20Northern%20Hemisphere