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

The correct answer is (a). The longest day of the year in the northern hemisphere is the summer solstice, which occurs on June 21 or 22. This is the day when the North Pole is tilted towards the sun, and the sun is at its highest point in the sky. The days are longer and the nights are shorter in the northern hemisphere after the summer solstice.

Option (b) is incorrect because the summer solstice does not occur in the second half of June. Option (c) is incorrect because the summer solstice does not occur in the first half of July. Option (d) is incorrect because the summer solstice does not occur in the second half of July.