Question

The following passage is adapted from an essay on the history of experimental low-temperature physics:

In April 1911, Dutch physicist Heike Kamerlingh Onnes and his research team at Leiden University conducted groundbreaking electrical resistance experiments on metals at cryogenic temperatures. Three years earlier, in 1908, Onnes had become the first scientist to liquefy helium, achieving a temperature of $4.2\text{ K}$ ($-268.95^\circ\text{C}$). This breakthrough allowed his team to systematically investigate how electrical resistance behaved in conductors near absolute zero.

Initial theoretical opinions regarding electrical conductivity at ultra-low temperatures were sharply divided among early twentieth-century physicists. Lord Kelvin had hypothesized that as temperature decreased toward absolute zero, conduction electrons would freeze in place, causing electrical resistance to increase toward infinity. Conversely, Onnes originally conjectured that electrical resistance would steadily diminish and smoothly approach zero as thermal motion ceased.

To test these competing hypotheses, Onnes and his assistant Gilles Holst constructed a closed glass capillary tube containing purified mercury. Mercury was selected because it could be repeatedly distilled to eliminate chemical impurities that might distort resistance measurements. The capillary tube was submerged in a double-walled bath of liquid helium inside a vacuum-insulated cryostat. As the team systematically reduced the vapor pressure over the liquid helium bath to lower the temperature, Holst monitored the potential difference across the mercury capillary using a sensitive Wheatstone bridge.

At a temperature of approximately $4.20\text{ K}$, the electrical resistance of the mercury sample did not drop gradually as Onnes had anticipated. Instead, within a temperature interval of less than $0.01\text{ K}$, the resistance plummeted abruptly from $0.11\text{ ohms}$ to less than one-hundred-thousandth of an ohm ($10^{-5}\text{ ohms}$), falling below the detection threshold of their instruments. Initially suspecting a short circuit in the wiring connections outside the cryostat, Holst and Onnes spent hours inspecting the external terminal leads before confirming that the mercury had entered a novel state of zero resistance, which Onnes subsequently named 'superconductivity' in 1912.

According to the passage, why did Kamerlingh Onnes and his team specifically choose mercury for their low-temperature electrical resistance experiments?