Entropy and enthalpy change on mixing liquids
This is difficult, because we do not know what is your current understanding and at what “level” of approximation you expect the question to be answered.

At a undergraduate level, or in the absence of any details (or thermochemical data or access to thermochemical tables), I would go with option (3).


Enthalpy: we are not given any indication at what is the enthalpy of mixing. In the simplest approximation, the enthalpy of mixing is zero, as in an ideal solution. It would correspond to a regime where the enthalpy of dissolution ($\Delta H_{\text{sol}}$) does not depend on the concentration of the solution. It's probably a good approximation, until you reach high concentrations.
Entropy: the entropy of mixture is positive, i.e. the process of mixing the two solutions is spontaneous. It can be explained by this reasoning.