Exercises targeting the core primarily work the muscles found in the:

Exercises that target the core primarily engage the muscles found in the abdomen. The core includes a group of muscles that stabilize, support, and move the trunk and pelvis. These muscles include not only the rectus abdominis (the "six-pack" muscle) but also the obliques, transversus abdominis, and the muscles in the lower back. A strong core is essential for maintaining balance, posture, and overall functional strength, which are crucial for various physical activities and daily movements.

The other options refer to muscle groups that are not the primary focus of core-targeting exercises. While arms, chest, and legs are involved in many physical activities and can be strengthened through different types of training, they do not represent the main area of focus when it comes to core exercises.