Final answer:
The 1) frontal lobe of the brain is the most undeveloped in terms of its functioning during infancy.
Step-by-step explanation:
The lobe of the brain that is most undeveloped in terms of its functioning during infancy is the frontal lobe. The frontal lobe is responsible for reasoning, motor control, emotion, and language. It contains the motor cortex, which is involved in planning and coordinating movement; the prefrontal cortex, which is responsible for higher-level cognitive functioning; and Broca's area, which is essential for language production.