Final answer:
The question appears to relate to material handling or engineering practices, particularly regarding crane operations. However, without specific context, it is impossible to define the exact percentage that constitutes a critical pick, which may vary by industry or company policy. Percent yield and selectivity from chromatography, while interesting, are unrelated to critical picks in lifting operations.
Step-by-step explanation:
A critical pick in reference to crane operations or material handling implies a lift that requires special attention due to its weight being a significant portion of the crane's total load capacity. However, the percentage that defines a critical pick may vary depending on the company's policy, industry standards, or regulations. In the absence of a specific context provided with the question, we cannot definitively state which percentage exceeds the threshold for being classified as a critical pick. If the question pertains to a standard or regulation, you would need to consult the relevant documentation or authority for the correct answer.
When discussing selectivity in chromatography, this concept is entirely different and involves the separation of compounds based on their interaction with the stationary and mobile phases. This is measured by the capacity factor of each peak. Selectivity would not generally be expressed as a percentage of the total load capacity, as it is not related to the concept of a critical pick in material handling or crane load management.
Concerning percent yield, which is related to chemistry, it is the ratio of the actual yield to the theoretical yield multiplied by 100. It's used to measure the efficiency of a chemical reaction or process. The specific percentages listed (e.g., 70%, 100%, etc.) represent different possible yields from chemical reactions but are not related to the concept of a critical pick in an engineering context.