Final answer:
A summer job at a coal mine may be illegal for a 16-year old due to exposure to hazardous substances, lack of safety training, and restrictions on working hours.
Step-by-step explanation:
A summer job at a coal mine can be illegal for a 16-year old due to several reasons. One reason is exposure to hazardous substances such as coal dust, which can cause health problems like black lung disease. Another reason is the lack of proper safety training for young workers, which can put them at risk of accidents and injuries. Additionally, there may be restrictions on extended working hours for minors to ensure their well-being and education.