Answer:
[tex]\large \boxed{\text{-273.1497 $^{\circ}$\text{C}}}[/tex]
Explanation:
[tex]\begin{array}{rcl}C & = & K - 273.15\\& = & 0.0003 - 273.15\\& = & \mathbf{-273.1497}\\\end{array}\\\text{Rhodium becomes superconducting at $\large \boxed{\textbf{-273.1497 $^{\circ}$\text{C}}}$}[/tex]