Explanation:

- Option 1: Malaysia

- Not the location of Southeast Asia's largest solar farm.

- Malaysia has solar initiatives but none leading the region in scale.

- Option 2: Vietnam

- Vietnam is home to Southeast Asia's largest solar farm.

- It has significantly invested in renewable energy, particularly solar.

- [] Correct Answer: Vietnam is where the largest solar farm is operational.

- Option 3: China

- While China leads globally in solar capacity, it is not in Southeast Asia.

- Hence, it isn't the location of the largest solar farm in Southeast Asia.

- Option 4: India

- India, though investing heavily in solar power, is not in Southeast Asia.

- Option 5: None of the above

- Incorrect because the largest solar farm is indeed in Vietnam.