d
આપેલી પરિસ્થિતિ \(\,\frac{Q}{t}\,\, = \,\,\frac{{KA\,\,({\theta _1} - {\theta _2})}}{\ell }\,\, = \,\,\) અચળ  \( \Rightarrow \,\,\frac{{{K_A}A\,({\theta _1} - \theta )}}{\ell }\,\, = \,\,\frac{{{K_B}A\,\,(\theta  - {\theta _2})}}{\ell }\)

\(\frac{{{K_A}}}{{{K_B}}}\,\, = \,\,\frac{{\theta  - {\theta _2}}}{{{\theta _1} - \theta }}\,\, = \,\,3\,\,\,\, \Rightarrow \,\,3\,{\theta _1} + {\theta _2} = \,\,4\,\theta \)

\(\because \,\,\,{\theta _1} - {\theta _2} = \,\,{20^ \circ }C\,\,\,\,\,\,\)

\(\therefore \,\,\,{\theta _2} = {\theta _1} - {20^ \circ }C\,\,\,\,\)

\( \Rightarrow \,\,3\,{\theta _1} + {\theta _1} - {20^ \circ }C\,\, = \,\,4\,\theta \,\,\,\,\,\,\, \)

\(\Rightarrow \,\,4\,\,({\theta _1} - \theta )\,\, = \,\,{20^ \circ }C\,\,\,\)

\(\Rightarrow \,\,{\theta _1} - \theta \,\, = \,\,{5^ \circ }C\)