Are slow isobaric processes necessarily reversible? All isothermal and adiabatic processes are reversible when carried out very slowly.
Is it true for the isobaric process too? As isobaric process can also be carried out very slowly.
 A: Reversible processes are processes in which the thermodynamic system changes from one state to another such that it stays in equilibrium throughout the change. Usually you can achieve this by making the change arbitrarily slow such that you never really 'break' away from equilibrium or the system stays arbitrarily close to equilibrium state. Of course what is 'slow' depends on the system under consideration.
Isobaric processes are processes that occur under constant pressure. So if we are able to control the change in other macroscopic parameters of the system such that they change slow enough, yes you can carry out isobaric process slowly and reversibly.
Say you are heating an ideal gas in some container whose volume we can control. We know that the heat gained by the system will increase temperature and pressure of the gas. And at equilibrium we know that it obeys the ideal gas equation 
$$P = \frac{nRT}{V}$$
So if you are heating it slow enough, the slight change in pressure can be offset by proportionally adjusting the volume in such a way that the overall pressure remains a constant. The process being slow ensures that the system is close to equilibrium state and varying the volume will ensure that the system is at constant pressure and thus isobaric.
