# Assume that one of the generation of quarks is massless then cp violation is still there in quark sector?

If one of the generation of quarks(say up and down) is massless then cp-violation is still there in quark sector?

Yes, nothing changes about the general rules if $m_u=m_d=0$. The CKM matrix is still the $SU(3)$ matrix transforming the up-type quark mass eigenstate to the up-electroweak-partners of the down-type quark mass eigenstates. The general CKM matrix distinguishes the phase.