Which of the following leads is associated with the right margin of the sternum at the 4th intercostal space?

The lead associated with the right margin of the sternum at the 4th intercostal space is V1. This lead is specifically positioned in the 4th intercostal space, just to the right of the sternum, allowing it to monitor electrical activity coming from the heart, particularly the right atrium and the interventricular septum.

Each of the other leads serves different positioning and purposes in the electrocardiogram framework. For instance, V2 is placed on the left side of the sternum in the 4th intercostal space, capturing more of the left side of the heart's electrical activity. V3 occupies a more central position on the chest wall, between V2 and V4, while V5 is located further out on the left side, at the anterior axillary line, capturing its respective left lateral heart activities. Thus, while each lead has its importance, V1 is specifically aligned to monitor the right side of the heart at the level indicated in the question.