  The necessary and sufficient criteria for violating the Mermin and Svetlichny
inequalities by arbitrary three-qubit states are presented. Several attempts
have been made, earlier, to find such criteria, however, those extant criteria
are neither tight for most of the instances, nor fully general. We generalize
the existing criteria for Mermin and Svetlichny inequalities which are valid
for the local projective measurement observables as well as for the arbitrary
ones. We obtain the maximal achievable bounds of the Mermin and Svetlichny
operators with unbiased measurement observables for arbitrary three-qubit
states and with arbitrary observables for three-qubit states having maximally
mixed marginals. We find that for certain ranges of measurement strengths, it
is possible to violate Mermin and Svetlichny inequalities only by biased
measurement observables. The necessary and sufficient criteria of violating any
one of the six possible Mermin and Svetlichny inequalities are also derived.
