The Sun Insurance Office Ltd. was one of the earliest insurance companies to operate in India during the British period.
Kolkata (then Calcutta) was the commercial capital and major trading hub under British rule.
Because of its strategic location and large presence of British businesses, Kolkata became the base for many insurance companies.
Sun Insurance Office Ltd. was established in Kolkata to serve marine and fire insurance needs for the British trading community and local merchants.
This set the stage for the expansion of insurance services in India.
Therefore, the correct answer is Kolkata.