What is the main reason that it takes 2 to 3 minutes for the reaction to occur between sucrose and sulfuric acid in the dehydration of sucrose?

 There is a time delay of almost two to three minutes before the reaction proceeds because of the following processes:

1)     The acid starts to go yellow as the dehydration begins.

2)     The rate of dehydration then accelerates as the acid heats up because the reaction is exothermic/chemical (releases energy by light or heat).  As the sugar molecules are stripped of water, the heat generated turns the water into steam which then expands the remaining carbon into a porous, smoking, black column.

3)    This expands out of the reaction vessel, producing a choking acrid vapor and the smell of burned sugar.

 At this stage, sulfuric acid is highly corrosive and will burn skin so one must avoid contact with it. 

c. because step up transformer steps up the input voltage i.e increases the input voltage  

the number of turns are greater on the secondary side of step up transformer  

transformer does not handle dc current