The concept of zero was indeed developed in India, but attributing it to a specific individual like Aryabhata, Varahamihira, or Bhaskara I (options 1, 2, and 3) is not accurate. Each of these scholars made significant contributions to mathematics, but there`s no concrete evidence to suggest that they specifically invented zero.

The concept of zero likely developed over time as part of the decimal place-value system in ancient Indian mathematics. It was a tool to denote the absence of value and to enable calculations with it. Existence of zero can be traced back to 7th century AD but its origins remain largely unknown.

So option 4 "an unknown Indian" is the most correct answer, as it likely developed as a part of broader mathematical evolution rather than the brainchild of a specific individual. It honours India`s pivotal role in creating zero while acknowledging that the exact origin is in dispute.