Option 1 states that both statements are individually true and that Statement II is the correct explanation of Statement I. Let`s analyze both statements separately to evaluate their accuracy.

Statement I claims that plantation farming has mostly been practiced in humid tropics. This statement is generally true. Plantation farming, which involves cultivating cash crops such as coffee, tea, rubber, and palm oil on large estates, has indeed been prevalent in humid tropical regions. The high temperatures and abundant rainfall in these areas provide suitable conditions for the growth of these crops.

Statement II suggests that the soil of humid tropics is highly fertile. This statement is false. While some areas within humid tropics may have fertile soil, it is not a characteristic of the entire region. The fertility of soil depends on various factors such as climate, topography, geology, and human interference. Therefore, it is not accurate to claim that the soil in the humid tropics is uniformly highly fertile.

Since Statement I is true (as discussed above), but Statement II is false, option 1 is not the correct answer.

Therefore, the correct answer is option 3, which states that Statement I is true, but Statement II is false.