the first question

 

2RMgX  +   RCOOR'  ------------------>   R₃COH  +  R'OH  +  Mg(OH)X

                                 hydrolysis

 

the second question...

 

the III and IV compound contain acidic proton..... so when grignard reagent is prepared from these compounds ... intra molecular reaction takes place.....

and so we cannot use it to prepare grignard reagent.....