Let mass of Na2CO3 and NaCl in given mixture be ′a′ and ′b′ g respectively.
∴a+b=4...(i)
The solution is allowed to react with HCl; only Na2CO3 reacts and thus, Meq. of Na2CO3= Meq. of HCl in 25 mL=50×(110)=5
∴ Meq. of Na2CO3 in 250 mL=(5×250)25=50
or, a1062×1000=50
∴a=2.65
By (i), b =4−2.65=1.35
∴Na2CO3=(2.654)×100=66.25%
and NaCl= 33.75%
So, answer is 34 %.