Question

nahco3+ch3cooh--> co2+h2o+nach3coo write (aq), (s), (l)

Answer 1

aq = aqueous (meaning it is solvated by water)
l = liquid phase
s = solid phase
g = gas phase

Answer 2

If you understand this reaction, then you would know it takes place in water

If g isn't an option I would assume you could write that the CO2 is kept in solution. It would make no sense to write aq next to H2O, why would you say water is dissolved in water?

Answer 3

or you could just not write anything next to CO2 either or