The correct answer is the following.
The treaty that placed a ceiling in the amount of nuclear weapons the United States and the Soviet Union could possess was “SALT I.”
The United States and the Soviet Union signed the firsts treaty to limit the amount of nuclear weapons. They were the SALT 1 and 2 treaties. SALT means Strategic Arms Limitation Talks. The first treaty was signed in 1972 and the other in 1979. The agreements tried to limit the production of intercontinental ballistic missiles that contained nuclear weapons. Formal negotiations started in November 1969 due to the initiative of United States President Lyndon B. Johnson.