Step 1: Recognized nuclear powers
- India conducted its first nuclear test in 1974 (Smiling Buddha) and is a nuclear weapons state.
- Pakistan became a nuclear weapons power in 1998 after its successful nuclear tests.
- China tested its first nuclear weapon in 1964 and is officially recognized as a nuclear power under the NPT (Non-Proliferation Treaty).
Step 2: Non-nuclear country
- Sri Lanka has never developed or tested nuclear weapons.
- It is a signatory to the NPT and advocates nuclear disarmament and peaceful use of nuclear energy.
Step 3: Analyzing the options
- India: Possesses nuclear weapons.
- Pakistan: Possesses nuclear weapons.
- China: Possesses nuclear weapons.
- Sri Lanka: Does not possess nuclear weapons.
Step 4: Conclusion
Thus, the correct answer is Sri Lanka.
\[
\boxed{\text{Correct Answer: (D) Sri Lanka}}
\]