Organic synthesis: compare question

An unknown organic compound, $\ce{C3H6O2}$, is treated with separate samples of sodium carbonate, Tollens' reagent, and bromine water. The observations are recorded.

1. With sodium carbonate, effervescence is seen.
2. With Tollens' reagent, no silver mirror forms.
3. With bromine water, the colour is unchanged.

Compare the information from the three tests to identify the functional groups present in the compound. In your answer, state the functional group responsible for each observation, and explain why the other two tests give the results they do.