Option 1 -> While GST combines multiple taxes, this makes it comprehensive, not unified.
Option 2 -> Incorrect, as other indirect taxes like customs duty still exist alongside GST.
Option 3 -> GST created a uniform tax structure replacing different state-level taxes with one standard system across India.
Option 4 -> Simplicity is not the defining feature of a unified tax system.
Hence, Option 3: Because it brought uniformity in tax rate across the country -> GST is called a unified tax system because it replaced the fragmented tax structure where different states had different indirect taxes and rates. Under GST, India adopted "One Nation, One Tax" principle, ensuring uniformity in tax rates and structure across all states, eliminating interstate tax barriers and creating a seamless national market. This uniformity in taxation across the country is what makes GST a truly unified tax system -> correct