Which medium is not currently used for data communication?

• A. Copper cables / electrical signals
• B. Hydrogen cables / electron ionisation
• C. Wireless / electromagnetic waves
• D. Fibre optics / pulses of light

Answer: (B)

Data communication relies on a physical path that can carry signals reliably, safely, and consistently. Copper cables with electrical signals are a long-established medium (used in Ethernet and phone networks), wireless transmission with electromagnetic waves is common for mobile and Wi‑Fi connections, and fiber optics use pulses of light for high-speed, long-distance data transfer. The option involving hydrogen cables and electron ionisation isn’t a practical data-transmission medium because there’s no stable, reliable way to use ionized hydrogen as a signal carrier. Gas-based transmission would be inefficient, prone to noise and instability, and dangerous due to flammability and high voltages needed to ionize the gas. In short, hydrogen cables aren’t used for data communication, making that option the correct choice.