Which of the following is mismatched?

The coefficient of thermal conductivity of copper is nine times that of steel. In the composite cylindrical bar shown in the figure,what will be the temperature at the junction of copper and steel in $^oC$?

In a reaction of $C_6H_5Y$,the major product $(> 60\%)$ is $m$-isomer,so the group $Y$ is:

Which of the following compounds on oxidation gives ethyl methyl ketone?

Which one of the following gives a straight line for Freundlich adsorption isotherm?

The angle between the lines joining the origin to the points of intersection of the line $x + 2y + 1 = 0$ and the curve $2x^2 - 2xy + 3y^2 + 2x - y - 1 = 0$ is