Which of the following computer devices are output devices only?

A. Track ball
B. CRT monitor
C. Number pad
D. Plotter
Choose the correct answer from the options given below:

The correct answer is B and D only — that is, the CRT Monitor and the Plotter are output devices only.

To understand why, let us examine the nature of each device listed in the question one by one.

A. Track Ball
A trackball is an input device. It is a pointing device used to move the cursor on a screen by rotating a ball with fingers or a thumb. Because it sends positional data into the computer, it is purely an input device. It produces no output for the user. Therefore, A is not an output-only device.

B. CRT Monitor
A CRT (Cathode Ray Tube) monitor is a classic output device. It receives processed data from the computer and displays it visually on screen — whether text, images, or video. The monitor does not send any data back to the computer; it only presents information to the user. Therefore, B is an output-only device. ✓

C. Number Pad (Numeric Keypad)
A number pad is an input device. It is used by the user to enter numeric data into the computer system. Since it feeds data into the computer and receives nothing back, it is purely an input device. Therefore, C is not an output-only device.

D. Plotter
A plotter is an output device. It is specifically designed to produce high-quality printed drawings, charts, blueprints, and vector graphics on paper or other media. The plotter only receives commands from the computer and produces physical hard-copy output — it sends no data back to the computer. Therefore, D is an output-only device. ✓

Summary Table:

Since only B (CRT Monitor) and D (Plotter) are exclusively output devices — meaning they only display or produce results from the computer and do not send any data into it — the correct answer is confirmed to be B and D only.