Chọn $Na$$*)NH_4Cl$
$2Na+2H_2O\rightarrow 2NaOH+H_2\uparrow$
$NaOH+NH_4Cl\rightarrow NaCl+NH_3\uparrow+H_2O$
Có khí mùi khai bay ra
$*)FeCl_2$
$2Na+2H_2O\rightarrow 2NaOH+H_2\uparrow$
$2NaOH+FeCl_2\rightarrow 2NaCl+Fe(OH)_2\downarrow$màu trắng xanh
$*)FeCl_3$
$...........$
$3NaOH+FeCl_3\rightarrow 3NaCl+FeCl_3\downarrow$màu đỏ nâu
$*)AlCl_3$
$3NaOH+AlCl_3\rightarrow 3NaCl+Al(OH)_3\downarrow$kết tủa keo
$NaOH+Al(OH)_3\rightarrow NaAlO_2+2H_2O$
$*)MgCl_2$
$MgCl_2+2NaOH\rightarrow MgCl_2+Mg(OH)_2\downarrow$màu trắng