Answer:
The options are
The layer never formed at location 2.
The locations were too close together.
The organism did not exist at location 2.
The missing layer at location 2 may have eroded.
The layers at location 2 formed much earlier than those at location 1.
The answer is
The layer never formed at location 2.
The organism did not exist at location 2.
The missing layer at location 2 may have eroded.
The most likely event in the case of an index fossil which is found in a layer at location 1 and not found at location 2 nearby which is known to be the same relative age indicates that the layer never formed at location 2, the organism did not exist at location 2, or the missing layer at location 2 may have eroded.