The correct answer is A. 15%.
A first class brick when immersed in cold water for 24 hours should not absorb water more than 15%. This is because the brick should be able to withstand the effects of water without becoming too heavy or weak. If the brick absorbs too much water, it will become more difficult to handle and may be more likely to break.
Option B, 20%, is too high. A brick that absorbs 20% of its weight in water will be significantly heavier and weaker than a brick that absorbs 15% of its weight in water.
Option C, 22%, is also too high. A brick that absorbs 22% of its weight in water will be even heavier and weaker than a brick that absorbs 20% of its weight in water.
Option D, 25%, is the highest of the four options. A brick that absorbs 25% of its weight in water will be very heavy and weak. It is likely to break if it is handled roughly.
Therefore, the correct answer is A. 15%.