In a B+ tree, the requirement of at least half-full (50%) node occupancy is…

Answer: Only the root node

Explanation:

• Minimum-occupancy rule: Except for the root, internal nodes must have at least about half the maximum number of children (typically ceil(m/2) children for order m), and leaf nodes must have at least about half the maximum number of entries.

• Root exception: The root node is allowed to be less than half full. If the root is internal it may have as few as two children; if the root is the only node (a leaf), it may contain between one and the maximum number of entries.

• Conclusion: Because only the root is permitted to violate the half-full requirement, the correct answer is that the rule is relaxed only for the root node.