I believe the best answer is false.
The statement, “The atonement of Christ pays for the sins of all mankind” conveys the idea that Christ redeems all men without condition. That’s the plan the adversary sought in the preexistence. That is why I believe the best answer is false.
The following scripture makes it clear that Christ suffered for all, but only those who repent receive the full blessings of the atonement.
For behold, I, God, have suffered these things for all, that they might not suffer if they would repent. D&C 19:16-17
In the next verse we learn that the wicked (those who don’t repent) remain as though there was no atonement, except that they will be resurrected.
Therefore the wicked remain as though there had been no redemption made, except it be the loosing of the bands of death. Alma 11:41
When I wrote the question for the quiz, I was thinking of a phrase that is heard often, “Christ died for the sins of all mankind.” That true, however, if we are not careful to add more detail it can be misleading, especially for youth and those who are new to gospel teachings. They can be left with the impression that God saves all men without conditions (That’s the plan the adversary promoted).
So the next time you hear someone say that Christ died for the sins of all mankind, I hope you will add, that true but only “on conditions of repentance”.
And there he preached to them the everlasting gospel, the doctrine of the resurrection and the redemption of mankind from the fall, and from individual sins on conditions of repentance. D&C 138:19