Final answer:
Hindi is the 'neutral' language that serves as the chief integrating language in South Asia's linguistic geography.
Step-by-step explanation:
The 'neutral' language that serves as the chief integrating language in South Asia's linguistic geography is Hindi. Hindi is widely spoken in the northern regions of South Asia and acts as a lingua franca among people with different native languages. It is the official language of the Indian government and is spoken by a large population across the region.