When was Nuclear Non-Proliferation Treaty (NPT) signed?

The correct answer is Option 1 - 1968

The US and Soviet Union signed a number of other arms control treaties including the Strategic Arms Limitations Treaty II or SALT II and the Strategic Arms Reduction Treaty (START). The Nuclear Non-Proliferation Treaty (NPT) of 1968 was an arms control treaty in the sense that it regulated the acquisition of nuclear weapons: those countries that had tested and manufactured nuclear weapons before 1967 were allowed to keep their weapons; and those that had not done so were to give up the right to acquire them. The NPT did not abolish nuclear weapons; rather, it limited the number of countries that could have them.