Step 1: Understanding the Concept.
This is a specific current-affairs fact about a military appointment in a Southeast Asian country with a notable ethnic Indian and Sikh community.
Step 2: Check the options.
Thailand, Malaysia, and Indonesia were not the country that made this appointment, so options A, C, and D are wrong.
Step 3: Final Answer.
Singapore appointed Brigadier General Ravinder Singh as its Chief of Army, making him the first Sikh to hold the post in nearly three decades, so option B is correct.