**Answer:**

The correct answer is option 'D', Touchpad.

A touchpad is a magnetic device that allows users to move the cursor on a computer screen by touching it with their fingers. It is a common input device found on laptops and some desktop computers. Let's explore why touchpad is the correct answer in detail.

**Touchpad:**

A touchpad is a small, flat surface typically located below the keyboard on a laptop. It uses sensors to detect the movement and position of the user's fingers. The touchpad surface is usually made of a material that allows for smooth tracking and easy finger movement.

**How it works:**

1. Electrostatics: A touchpad uses the principles of electrostatics to detect the position of the user's fingers. When you touch the touchpad with your finger, it creates an electrostatic field disturbance, which is detected by the sensors.

2. Capacitive Touch: Most touchpads use capacitive touch technology. They have a grid of tiny capacitors beneath the touchpad surface. When a finger touches the surface, it changes the capacitance of the specific capacitors, which is then measured and used to determine the position of the finger.

3. Movement Tracking: As you move your finger across the touchpad surface, the sensors detect the changes in capacitance and translate them into cursor movement on the screen. The speed and direction of your finger movement determine the speed and direction of the cursor.

**Advantages of a Touchpad:**

- Portability: Touchpads are commonly used on laptops because they are compact and integrated into the device. This makes them highly portable and allows for easy navigation without the need for an external mouse.

- Multitouch Gestures: Many touchpads support multitouch gestures, allowing users to perform various actions such as scrolling, zooming, and rotating by using specific finger movements on the touchpad surface.

- Customization: Touchpad settings can often be customized to suit individual preferences. Users can adjust the sensitivity, cursor speed, and other settings to optimize their experience.

**Conclusion:**

In conclusion, a touchpad is a magnetic device that allows users to move the cursor on a computer screen by touching it with their fingers. It uses electrostatics and capacitive touch technology to detect finger movements and translate them into cursor movements. Touchpads are commonly found on laptops and provide a portable and convenient way to navigate the computer screen without the need for an external mouse.