Option 1 -> Aryabhata was an ancient Indian mathematician who approximated pi but is not known for infinite series formulas.
Option 2 -> C. V. Raman was a physicist who won the Nobel Prize for the Raman Effect, not a mathematician working on pi.
Option 3 -> Srinivasa Ramanujan was a mathematical genius who discovered several groundbreaking infinite series for pi.
Option 4 -> P. C. Mahalanobis was a renowned statistician, not known for work on pi.
Hence, Srinivasa Ramanujan -> He discovered numerous rapidly converging infinite series for pi in the early 20th century, some of which form the basis of modern algorithms used to calculate pi to billions of digits -> correct