Final answer:
In welding, the filler rod should be added to the leading edge of the molten pool in a tee joint to ensure a uniform and strong weld.
Step-by-step explanation:
In the context of welding, particularly when working with a tee joint, the addition of filler rod is an integral part of the process to ensure a strong bond between the pieces being joined. The filler rod should be added to the leading edge of the molten pool. During the welding process, the molten pool is the area where the base metals melt and fuse together, sometimes with the addition of the filler material. By adding the filler rod to the leading edge, you ensure that it melts consistently into the pool, allowing for a uniform and strong weld joint.