## Chemistry and Chemical Reactivity (9th Edition)

$NaHCO_3, KHCO_3, CaCO_3$
The compounds $NaHCO_3, KHCO_3, CaCO_3$, when reacting with HCl, would produce carbonic acid, which breaks into water and gaseous carbon dioxide, therefore gas-forming reactions. The other two compounds, $Al(OH)_3, Mg(OH)_2$, are bases, therefore their reaction with HCl is an acid-base reaction.