Step 1: Understanding the events in order.
- The Korean War occurred from 1950-1953, making it the first event.
- The Strategic Arms Limitation Talks-I (SALT I) were held in 1972 to limit nuclear arms.
- The Non-Proliferation Treaty (NPT) was signed in 1968 to prevent the spread of nuclear weapons.
- The Vietnam War took place from the 1950s to 1975, but it began after the Korean War.
Step 2: Arranging the events chronologically.
- (A) Korean War (1950-1953)
- (D) Strategic Arms Limitation Talks-I (1972)
- (C) Non-Proliferation Treaty (1968)
- (B) Vietnam War (1955-1975)
Step 3: Conclusion.
The correct order is (2) A, D, C, B.