If a metal changes color over time from exposure to air, what has likely occurred?

Modern weaponry has increased the number of deaths in wars and violent conflicts.

The atomic number, or number, is the described as the number of in the nucleus of an chemical element.

Large helium-filled balloons are used to lift scientific equipment to high altitudes. what is the pressure inside such a balloon if it starts out at sea level with a temperature of 10.0ºc and rises to an altitude where its volume is twenty times the original volume and its temperature is – 50.0ºc ?