\(n_{K_2CO_3}=\dfrac{4.14}{138}=0.03\left(mol\right)\)
\(n_{HCl}=0.2\cdot0.35=0.07\left(mol\right)\)
\(K_2CO_3+2HCl\rightarrow2KCl+CO_2+H_2O\)
\(0.03..........0.06.........0.06.......0.03\)
\(V_{CO_2}=0.03\cdot22.4=0.672\left(l\right)\)
\(n_{HCl\left(dư\right)}=0.07-0.06=0.01\left(mol\right)\)
\(C_{M_{HCl\left(dư\right)}}=\dfrac{0.01}{0.2}=0.05\left(M\right)\)
\(C_{M_{KCl}}=\dfrac{0.06}{0.2}=0.3\left(M\right)\)