In a chemical reaction, temperature coefficient will be least in the temperature range of 

$\begin{array}{l}\log \frac{{\mathrm{K}}_2}{{\mathrm{K}}_1}=\frac{{\mathrm{E}}_{\mathrm{a}}}{2.303\mathrm{R}}\left[\frac{{\mathrm{T}}_2-{\mathrm{T}}_1}{{\mathrm{T}}_1{\mathrm{T}}_2}\right]\\ \mathrm{In}\mathrm{all}\mathrm{cases}{\mathrm{T}}_2-{\mathrm{T}}_1=10\mathrm{K}\\ \log \frac{{\mathrm{K}}_2}{{\mathrm{K}}_1}\propto \frac{1}{{\mathrm{T}}_1{\mathrm{T}}_2}\\ \mathrm{Higher}\mathrm{the}\mathrm{product}\mathrm{of}{\mathrm{T}}_1{\mathrm{T}}_2,\text{\hspace{0.17em}\hspace{0.17em}less}\mathrm{er}\mathrm{the}\mathrm{value}\mathrm{of}\frac{{\text{K}}_2}{{\text{K}}_1}\end{array}$