The correct answer is: B. May
The length of a day is determined by the Earth’s rotation on its axis. The Earth’s axis is tilted at an angle of 23.5 degrees relative to its orbital plane. This tilt causes the Earth to experience seasons. In the Northern Hemisphere, the days are longer in the summer and shorter in the winter.
Bihar is located in the Northern Hemisphere. The summer solstice in Bihar occurs on June 21st. On this day, the Northern Hemisphere is tilted towards the sun, and the days are longest. The winter solstice in Bihar occurs on December 21st. On this day, the Northern Hemisphere is tilted away from the sun, and the days are shortest.
Therefore, the month with the longest days in Bihar is May.
Option A: January is a winter month in the Northern Hemisphere. The days are shorter in winter than in summer.
Option B: May is a summer month in the Northern Hemisphere. The days are longest in summer.
Option C: June is also a summer month in the Northern Hemisphere. The days are long in June, but not as long as in May.
Option D: December is a winter month in the Northern Hemisphere. The days are short in winter.