Final answer:
The serious sins in the Catholic faith that break a Christian's relationship with God and condemn them to Hell if they go unconfessed and if penance is not completed before death are called Mortal sins.
Step-by-step explanation:
The serious sins in the Catholic faith that break a Christian's relationship with God and condemn them to Hell if they go unconfessed and if penance is not completed before death are called Mortal sins. These sins are considered to be the most severe and require the sacrament of confession to be forgiven.