ANS:B - >100

Superconductivity in metals is observed at temperatures below 100 Kelvin (°K). Superconductivity is a phenomenon where certain materials exhibit zero electrical resistance and the expulsion of magnetic fields when cooled below a critical temperature, known as the transition temperature or critical temperature. Initially, superconductivity was observed only at very low temperatures close to absolute zero (0 Kelvin or -273.15°C). However, advancements in materials science have led to the discovery of materials that exhibit superconductivity at higher temperatures, known as high-temperature superconductors. For the options provided:

• <100 °K: This option aligns with the correct temperature range for observing superconductivity.
• >100 °K: Superconductivity is typically observed at temperatures lower than 100 Kelvin, so this option is incorrect.
• about 273 °K: 273 Kelvin corresponds to 0°C, which is above the critical temperature for most known superconductors. Hence, this option is incorrect.
• about 373 °K: 373 Kelvin corresponds to 100°C, which is much higher than the critical temperature for superconductivity. Therefore, this option is incorrect.