2/
$PTPƯ:$
$2Na+2H_2O\xrightarrow{} 2NaOH+H_2↑$
$Ba+2H_2O\xrightarrow{} Ba(OH)_2+H_2↑$
$CaO+H_2O\xrightarrow{} Ca(OH)_2$
$SO_2+H_2O⇄H_2SO_3$
3/
$a,C\%_{KCl}=\dfrac{20}{600}.100\%=3,33\%$
$b,CM_{MgCl_2}=\dfrac{0,5}{1,5}=0,33M.$
$c,m_{muối ăn}=200.10\%=20g.$
$⇒m_{H_2O}=200-20=180g.$
chúc bạn học tốt!