What is the mass in gram of 1 atom of an element if its atomic mass is $$10 ~\mathrm{u}$$ ?

How many gram of H$$_2$$O are present in 0.25 mol of it?

What is percentage atom economy during conversion of reactant to product if formula weight of reactants is 246 u and of product is 123 u?

Identify the change in colour when $$\mathrm{NaCl}$$ solution is titrated against $$\mathrm{AgNO}_3$$ solution using fluorescein indicator.