The temperature of inversion of a thermocouple is 620^ C and the...

The temperature of inversion is higher than the neutral temperature by the same amount as the neutral temperature is higher than the temperature of cold junction. As per Key Idea $t_n-t_0=t_i-t_n \Rightarrow t_0=2 t_n-t_i$ Given, $t_i=620^{\circ} \mathrm{C}, t_n=300^{\circ} \mathrm{C}$ Hence, $t_0=$ temperature of cold junction $$\begin{aligned} & =2 \times 300-620 \\ & =600-620=-20^{\circ} \mathrm{C}\end{aligned}$$ NOTE: Neutral temperature does not change for a metal whether the temperature of cold junction and inversion temperature change by any value.