To find out how many employees participated in the training, we can use the given employee to instructor ratio of 12 to 2.
First, we need to simplify the ratio: \[ \frac{12}{2} = 6 \] This means there are 6 employees for every 1 instructor.
If there are 40 instructors, we can set up the following calculation to find the number of employees: \[ \text{Number of employees} = \text{Number of instructors} \times 6 = 40 \times 6 = 240. \]
So, the total number of employees who participated in the training is \( \textbf{240} \).
The answer is B. 240.