https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_classes_perms_enforcing.htm

"Apex generally runs in system context; that is, the current user's permissions and field-level security aren’t taken into account during code execution. "

B is the correct answer.
Normally, we can use REST API (A), but in this scenario user do not have permission to edit geolocation field. (REST API run as user permission)
We should use REST Apex as a customize solution since we can configure the Connected app to have permission to edit geolocation field.

B is the correct answer.
Normally, we can use REST API (A), but in this scenario user do not have permission to edit geolocation field. (REST API run as user permission)
We should use REST Apex as a customize solution since we can configure the Connected app to have permission to edit geolocation field.

A. The mobile device makes a REST API inbound call - This option is correct as it meets the requirement of obtaining the GPS coordinates and storing it in a custom geolocation field in Salesforce. REST API calls can be used to retrieve and update data from Salesforce, making it a suitable option for this scenario.