Compound (A) reacts with CuNH32+ and Tollens reagent, but after reaction with alc. KOH it does not give the above test. Compound (A) is:

Terminal alkyne containing four or more C atoms on reaction with alk. KOH isomerises to internal alkynes, which do not give all the tests mentioned. Although (2) and (4) are also terminal alkynes, they do not have sufficient C atoms to be converted to internal alkynes. So the answer is (3).