Respuesta :
The third reaction will form a gaseous product, COâ‚‚
KHCO₃ + HBr → KBr + H₂O + CO₂
KHCO₃ + HBr → KBr + H₂O + CO₂
The  reaction that would result  in formation  of gaseous product  is
KHCO3  +  HBr  ( third  answer)
explanation
KHCO3  react with  HBr  to form  KBr ,  CO2  and H2O  according  to  the  below equation.
KHCO3 + HBr →  KBr  + CO2 + H2O
CO2 ( carbon (IV)  oxide)  is the gas that  is  formed  during  reaction.
other reaction does not produce a  a gas for example  NaOH +  HCl forms  NaCl  and H2O