Hi Bob, Intel® Core processors can handle multiple tasks simultaneously. The usage of the processor cores depends on the application(s) running, the power settings and how they are managed by the operating system.
The graphics show four cores being used; one of them is used more than the rest. It is perfectly normal for an Intel® processor if a single core shows more utilization than the rest of them.
For information about the exact Intel® processor model included with your system we suggest you contacting Apple*.