Question

convert benzene into metadichlorobenzene

Answer 1

 1: NITRATION 

C6H6 + NO2 ----> C6H5(NO2) 

STEP 2: CHLORINATION 

C6H5(NO2) + Cl ----> C6H4(NO2)(Cl) [1-chloro-3-nitrobenzene] 

STEP 3: Formation of amine 

Reduction of nitro compound to amine is done by reaction of nitro compound by passing hydrogen gas in presence of Fe/HCl. 

C6H4(NO2)(Cl) ----Fe-HCl-----> C6H4NH2(Cl) 

Now proceed Diazotiazation and Sandmeyer's reaction 
hope it helps u