Step 1: Understanding Kant's Postulates of Morality.
Immanuel Kant, in his moral philosophy, identifies certain postulates or necessary assumptions for morality:
- C. Freedom of Will: For Kant, moral responsibility assumes that individuals have the freedom to act according to their rational will.
- D. Existence of God: Kant believed that the existence of God is a necessary postulate for the moral law to make sense, as God ensures the ultimate justice.
- A. Mortality of Soul and B. Immortality of Soul are not directly related to Kant's postulates of morality.
Step 2: Conclusion.
The correct answer is 2. C and D only.
Final Answer:
\[
\boxed{\text{The correct answer is 2. C and D only.}}
\]