The gas which is used to produce and sustain powerful superconducting magnets, which form an essential part of Magnetic Resonance Imaging (MRI) system is:

Helium

The correct answer is option 3. Helium.

Here is an explanation of why helium is used for cooling superconducting magnets in MRI systems:

Superconducting Magnets in MRI

Superconductivity: Superconductors are materials that can conduct electricity with zero electrical resistance when cooled below a certain critical temperature. This property is crucial for creating the strong and stable magnetic fields required in MRI machines.

Cooling Requirement: To maintain superconductivity, superconducting magnets need to be kept at extremely low temperatures. At higher temperatures, these materials lose their superconducting properties and start to exhibit electrical resistance.

The reason for the use of helium is:

Low Boiling Point: Helium is chosen for its extremely low boiling point. Liquid helium boils at around 4 Kelvin (−269°C or −452°F), which is much lower than the temperatures required to achieve superconductivity in many materials used for MRI magnets. This low temperature is essential because it allows the superconducting magnets to operate without resistance, enabling them to produce very strong magnetic fields.

Stable and Efficient Cooling: Liquid helium has a high thermal conductivity, making it effective in transferring heat away from the superconducting coils. This helps maintain the low temperatures required for superconductivity. Helium remains in a liquid state at temperatures necessary for superconductivity, whereas other gases like oxygen or nitrogen would not remain in a liquid state at these temperatures.

Other Gases:

Oxygen: Has a boiling point of around -183°C (90 K). It is not cold enough to maintain the necessary temperatures for superconductors.

Neon: Boils at about -247°C (26 K). While it’s colder than many other gases, it's still not as effective as helium for the temperatures needed for superconductivity.

Argon: Boils at about -186°C (87 K). Like oxygen, it doesn’t provide the low temperatures necessary for superconductors.

In summary, helium is used because its boiling point is low enough to ensure that superconducting magnets remain below their critical temperature, maintaining their superconducting state and enabling MRI machines to function effectively.