$1.($a$)$A measured value of sheet resistance after pre$-$deposition was found to be in the order of$1200-$o$.$ The sheet resistance value after drive$-$in process was observed to be in the order of$80-$o$.$ Find the correct reason and justify the answer.$($i$)$ The impurities are diffused in the bulk.$($ii$)$ The mobility improvement due to transformation of interstial diffusion to substitutiondiffusion.$($iti$)$ The junction depth changed due to drive$-$in process. $($iv$)$ None.