Final answer:
The correct option B) willful violation. An OSHA inspector observing a worker not using fall protection on a construction site would be considered a serious violation, specifically categorized as a willful violation.
Step-by-step explanation:
An OSHA inspector observing a worker not using fall protection on a construction site would be considered a serious violation of OSHA standards. Regarding the options given, this violation is specifically categorized as a willful violation (Option B).
Willful violations are the most severe and occur when an employer intentionally and knowingly disregards OSHA standards and regulations, resulting in a hazardous workplace.