The correct answer is: B. number of employees.
The number of employees is the most common basis for apportioning welfare department expenses. This is because the number of employees is a good indicator of the amount of work that a department does. A department with more employees will typically have more work to do and will therefore need to spend more money on welfare.
The other options are not as good indicators of the amount of work that a department does. Wages are not a good indicator because they can vary depending on the salaries of the employees. Materials consumed are not a good indicator because they can vary depending on the type of work that the department does. The number of machineries is not a good indicator because it can vary depending on the technology that the department uses.
In conclusion, the number of employees is the best basis for apportioning welfare department expenses.