$X_1: Na$
$X_2: NaOH$
$X_3: Na_2SO_4$
$X_4: Cl_2$
$X_5: HCl$
$X_6: BaCl_2$
$Y_1: H_2O$
$Y_2: SO_3$
$Y_3: H_2$
$Y_4: BaO$
PTHH:
$(1) 2NaCl\buildrel{{đpnc}}\over\to 2Na+Cl_2$
$(2) 2Na+2H_2O\to 2NaOH+H_2$
$(3) 2NaOH+SO_3\to Na_2SO_4+H_2O$
$(4) 2Na+Cl_2\to 2NaCl$
$(5) Cl_2+H_2\buildrel{{t^o}}\over\to 2HCl$
$(6) NaOH+HCl\to NaCl+H_2O$
$(7) BaO+2HCl\to BaCl_2+H_2O$
$(8) BaCl_2+Na_2SO_4\to BaSO_4+2NaCl$
