In India, For Which Achievement is the Gupta Golden Age Best Known

(1) Adoption of the Printing press

(2) Invention of the Iron Foot Stirrup

(3) Use Of Gun Powder

(4) Development of the concept of zero

The answer is # 4 they develped the concept of zero in the use of math and also created the decimal system based on the number 10, the Arabic number system, a number writing system used all over the world today

I believe the answer is: (4) Development of the concept of zero

The concept was developed by the studies from various scholar, most notably a mathematician named Aryabhata and it become the basis that is used for modern mathematics that we see today.

This concept would even play a more crucial role int the field of engineering because due to the use of 1 and 0 as binary numbers.