How to evaluate the hardness of a Multiobjective Optimization problem?



Is it the concept of NP-complete still applied on the MOP
(Multiobjective Optimization)?

I do not know how to decribe decision version of the Multiobjective
Optimization problem even if we have two objectives say, A and B.

Could you give me an example?

Since a MOP can be usually formulated as an Integer Programming, it is
at least NP-hard, right?

Thanks for any advice!
.