Question

You feel every citizen has the right to own a gun. If you argue for that right based on the Constitution,

Answer 1

If you feel that every citizen has the right to own a gun and you argue for this based upon the Constitution. You are most likely referring to the "right to bear arms" which is written in Amendment II of the Constitution or the Second Amendment. 

Answer 2

A. Amendment II.

The Amendment II of the U.S. Constitution states the following:

A well regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms, shall not be infringed.

From all the options, this amendment is the one that is most likely to provide a very good groundwork for defending American's right to own a gun, even though nowadays, there is still a debate over what the intended aim of the Amendment was. Did it focus on protecting the private right of individuals to keep and bear arms, or militia organizations' right to keep and bear arms?