Both statements I and II are individually true, and statement II is the correct explanation of statement I.

Statement I states that chemical weathering processes are more active in hot and humid environments. This is true because higher temperatures can increase the rate of chemical reactions, while increased humidity provides more water for these reactions to occur.

Statement II states that high temperature and rainfall help in the process of decomposition of rocks. This is also true because high temperatures can speed up the chemical reactions that break down rocks, while rainfall provides water that can dissolve minerals and carry them away.

The relationship between the two statements is that the higher temperatures and increased rainfall in hot and humid environments contribute to the acceleration of chemical weathering processes, resulting in the decomposition of rocks.

Therefore, the correct answer is option 1, where both statements are true and statement II correctly explains statement I.