During the cold war, the notion of kept both the united states and the soviet union from using their nuclear weapons, but also kept each on constant alert in case the other dared to act first.

The correct answer is Mutual assured destruction

This means that both sides knew that if they started a war that they couldn't win because everything would be destroyed. There was no way for them to start a nuclear war and win without being obliterated by nukes from the opposite sides, so they just gathered their weaponry and didn't attack each other.

It turns into vapor and goes into the atmosphere

Ithink the answer is b : )