Hi,

 

Q.2 Here,

           2NaHCO₃  =>  Na₂CO₃   +   H₂O   +   CO₂   

        Sodium carbonate is stable and does not break on heating.

       Wt. lost = Wt. of carbon dioxide produced = 0.248 gm

       Now, calculate moles of carbon dioxide produced.

        Now, moles of sodium hydrogencarbonate present = 2*moles

                                       of carbon dioxide.

        Calculate wt. of sodium hydrogencarbonate. And, then you can get the composition of the mixture.