The US and Soviet Union signed a number of arms control treaties during the Cold War. Out of them which treaty was signed in the year 1968?

NPT

The correct answer is Option 4 - NPT

Option 1- SALT II
Option 2- START-I
Option 3- LTBT
Option 4- NPT

NPT (NUCLEAR NON-PROLIFERATION TREATY) was signed in Washington, London, and Moscow on 1 July 1968.

NUCLEAR NON-PROLIFERATION TREATY (NPT): Allows only the nuclear weapon states to have nuclear weapons and stops others from acquiring them. For the purposes of the NPT, a nuclear weapon state is one which has manufactured and exploded a nuclear weapon or other nuclear explosive device prior to 1 January 1967. So there are five nuclear weapon states: US, USSR (later Russia), Britain, France and China. Signed in Washington, London, and Moscow on 1 July 1968.

Remaining options:

SALT II (Strategic Arms Limitation Talks II):
Signed: 1979
Details: The treaty was signed by the United States and the Soviet Union to limit the number of strategic arms. Although it was signed, it was never formally ratified by the United States Senate.

START-I (Strategic Arms Reduction Treaty):
Signed: 1991
Details: This treaty was signed by the United States and the Soviet Union (later Russia) to reduce and limit strategic offensive arms. It was a significant step in arms control and marked the end of the Cold War era.

LTBT (Limited Test Ban Treaty):
Signed: 1963
Details: The treaty was signed by the United States, the Soviet Union, and the United Kingdom to prohibit nuclear weapon tests in the atmosphere, outer space, and underwater. It aimed to reduce the environmental contamination from nuclear testing.