Lithium, Sodium, Potassium; any of the Alkali Metals, which are farthest left on the periodic table. This is because they only have one electron in their outermost shell, so they would rather lose an electron rather than try to gain 7 to achieve that full outer shell.
Before the bullet is fired the momentum is Zero because nothing is moving but once the bullet is shot the momentum increases because of the movement of the bullet moving forward.
