Primary succession is development of communities in

The correct option is D Newly exposed unoccupied habitat
Ecological succession is a gradual process that involves a sequential change in the composition of species leading to the establishment of a stable community.

Based on the nudity of the area, succession is of two types as follows:

• Primary succession
• Secondary succession

Succession where a newly formed area is colonised for the first time by a group of species or living organisms is called primary succession. Such areas would have never been previously inhabited; it is barren and lacks fertile soil. For example, newly exposed unoccupied habitat.

Succession where natural communities develop in an area that was earlier occupied by living organisms that somehow were lost is called secondary succession. It begins in areas where natural biotic communities have been destroyed such as in cleared forest areas, freshly harvested crop fields, and ponds filled after a dry season.

Hence the correct option is
a. Newly exposed unoccupied habitat