What type of line indicates that the instrument is mounted in the field?

The correct choice indicates that a single line is used to represent instruments that are mounted in the field. This convention is widely adopted in instrumentation diagrams and drawings to clearly distinguish field-mounted devices from those that are installed in a control room or other locations.

Field-mounted instruments often have specific requirements concerning environmental conditions, accessibility for maintenance, and ruggedness, which are implied by their single line representation. By using this visual cue, engineers and technicians can quickly identify where devices are physically located, which aids in troubleshooting and maintenance activities.

In contrast, other line types may represent different placements or statuses of instruments, such as in control rooms or other non-field environments. Understanding these representations helps personnel effectively interpret diagrams used in process control and instrumentation.