In the northern hemisphere, the longest day of the year normally occurs in the:

1. A

   First half of the month of June

   First half of June. Solstice is around 21 June.

2. B

   Second half of the month of June

   Second half of June. Northern summer solstice ~21 June — longest day.

3. C

   First half of the month of July

   First half of July. After the solstice, days are already shortening.

4. D

   Second half of the month of July

   Second half of July. Further past the peak.

Summary. Official key is (b) second half of June. In the northern hemisphere the longest day is the June solstice, about 21 June, which falls in the second half of the month.