Does baking soda and lemon juice create a balloon to blow up?

Yes it can, the chemical reaction creates co2 which will go in the balloon therefore it will blow up.

yes and no.

because the gases in both of them react to eachother.

yes becuase balloons smell of polos

Conservation of mass and energy.You put in a certain amount of one or more reactants and if there is a chemical change, the new substance(s) will have net same mass-- Whether or not you can see it....