\(n_{Cl_2}=\dfrac{1,12}{22,4}=0,05\left(mol\right)\\ Cl_2+2NaOH\rightarrow NaCl+NaClO+H_2O\\ C_{MddNaOH\left(dư\right)}=0,05\left(mol\right)\Rightarrow Tính.theo.Cl_2\\ n_{NaOH\left(P.Ứ\right)}=2.n_{Cl_2}=2.0,05=0,1\left(mol\right)\\ n_{NaOH\left(dư\right)}=0,2.0,05=0,01\left(mol\right)\\ \Rightarrow C_{MddNaOH\left(ban.đầu\right)}=\dfrac{0,1+0,01}{0,2}=0,55\left(M\right)\\ \Rightarrow Chọn.D\)