Weathering is defined as the breaking down of soil, rocks, wood, minerals and artificial materials due to contact with the atmosphere of the Earth and water.
If a set of metal tools is left outside in the rain for long time, due to moisture the surface of metal gets corroded. Due to the presence of dissolved gases or chemicals in the rain, it is acidic in nature and known as acid rain. These chemicals can react with metal surface and changes the chemical composition of the metal tools. This results in corrosion or rusting of metal making it mechanically weak.
Therefore, metal tools gets corroded if left in the rain for a long time.