In computer hardware maintenance, Electrostatic Discharge (ESD) typically causes the most damage to which component, and why are its internal parts especially vulnerable compared to other peripherals?

Introduction / Context:
ESD (Electrostatic Discharge) is a sudden flow of electricity between two charged objects. In computer servicing and assembly, understanding which parts are most vulnerable is essential to prevent invisible, cumulative damage that leads to intermittent faults or total failure.

Given Data / Assumptions:

• Typical PC components considered: power supply, expansion board, monitor, and keyboard.
• Normal bench environment without specialized ionization unless stated.
• Human body can carry thousands of volts of static charge that discharge upon contact.

Concept / Approach:
ESD damage correlates with the presence of small-geometry semiconductor junctions and exposed circuitry. Components with dense ICs, unshielded traces, and direct handling risk are more susceptible. Expansion boards (e.g., graphics, NIC, sound cards) have numerous sensitive ICs and edge connectors directly touched during installation, making them prime ESD targets.

Step-by-Step Solution:

Verification / Alternative check:
Service guides and ESD handling standards emphasize antistatic bags, wrist straps, and grounded mats specifically when handling PCBs and add-in cards, confirming their heightened susceptibility.

Why Other Options Are Wrong:

• Power supply: Typically shielded, with fewer direct-contact ICs exposed during routine handling.
• Monitor: Enclosed; ESD rarely affects internal boards unless opened.
• Keyboard: Contains simple circuitry and is externally insulated.
• None of the above: Incorrect because expansion boards are clearly vulnerable.

Common Pitfalls:
Assuming visible sparks are needed for damage (latent ESD can occur below human perception), and touching card contacts without grounding.

Final Answer:
Expansion board