Option 1 states that both the assertion and reason are true, and that the reason is the correct explanation for the assertion. In this case, the assertion is that in humid tropical climatic areas, undissolved aluminium, iron, and manganese accumulate and make the soil unfertile. The reason given is that high bacterial activity destroys humus.

Both the assertion and reason are actually true. In humid tropical climates, with high temperatures and heavy rainfall, weathering and leaching of minerals often occur. This can lead to the accumulation of undissolved aluminium, iron, and manganese in the soil, which can adversely affect its fertility. However, the reason given is not the correct explanation for this phenomenon. High bacterial activity may contribute to the decomposition of organic matter and the release of nutrients from the soil, but it is not directly related to the accumulation of undissolved metals in the soil.

Therefore, while both the assertion and reason are true, the reason is not the correct explanation for the assertion. Hence, option 1 is incorrect. The correct answer should be option 2.