The executive department that deals most with foreign countries is

the department of defense.
the department of state.
the department of labor.
the department of commerce.

The department of state

The Department of State

Explanation:

The Department of State which is led by the secretary of the state is known to be an agency that deals with foreign policy of the country including travels, immigration and business deals or relations. Thus, it oversees the affairs of the country’s relationship in regard to negotiation and agreement with other countries.

in physics and chemistry, the law of conservation of mass or principle of mass conservation states that for any system closed to all transfers of matter and energy, the mass of the system must remain constant over time, as the system's mass cannot change, so quantity can neither be added nor be removed. Wikipedia

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