In titration we take, we take a reactant (titrand) in conical flask. The second reactant (titrant) is filled in burette.
Now we add indicator in the first reactant (taken in flask) and start adding the second reactant from burette.
The reaction starts and when it appears that we are approaching the end point, we start adding the second reactant slower, in order to avoid missing the end point. If we add the second reactant fast, it may lead to addition of excess of reagent and thus may affect our calculations and readings.
The answer is really simple, because if you have 1 nonmetal element that has a subscript of 2, you need to multiply the product and the first reactant by 2 to balance it.
