The concept of zero, the expansion of the caste
system, and the creation of the decimal system
are most closely associated with the
(1) inca empire (3) song dynasty
(2) tokugawa shogunate (4) gupta empire

These concepts associated with Gupta Empire (4) . The caste system generally is an Indian phenomenon and out of the options only 4 is an Indian government. Also, the concept of zero famously originates from India, too.