
The reaction shown is a free radical halogenation reaction. This method is unsuitable for the preparation of fluoroarenes because of the high reactivity of fluorine. Fluorine is so reactive that it is difficult to control the reaction, leading to multiple substitutions. In this reaction, the free radical is formed by using the metal Fe in dark conditions. For the other halogens, the reaction can be controlled to obtain the corresponding haloarenes.


Three identical heat conducting rods are connected in series as shown in the figure. The rods on the sides have thermal conductivity 2K while that in the middle has thermal conductivity K. The left end of the combination is maintained at temperature 3T and the right end at T. The rods are thermally insulated from outside. In steady state, temperature at the left junction is \(T_1\) and that at the right junction is \(T_2\). The ratio \(T_1 / T_2\) is 
