Question

The 38th parallel in Korea and the 17th parallel
in Vietnam were used to mark
(1) boundaries created by mountain ranges
(2) demarcation lines instituted by papal authority
(3) territorial claims disputed between ethnic
minorities
(4) political divisions established between
communist and noncommunist territories

Answer 1

The 38th parallel in Korea and the 17th parallel in Vietnam were used to mark "(4) political divisions established between communist and noncommunist territories", since the two countries in question are North and South Korea, which are still deep in conflict. 

Answer 2

The correct answer is (4) political divisions established between
communist and noncommunist territories

In Korea, it split the country between the North Koreans who were communists and the southerners who were capitalists, while in Vietnam it split them also into Northern communists and Southern non-communists. However, in Vietnam the communists eventually won while in Korea the parallel still exists today and the country is split.