Find the odd one out. Give a reason for your choice

1. Second, minute, hour,light year
2. kilogram ,gram, milligram ,micron
3. meter, kilometere ,micron ,milligram

Light Year : All others are time. This is the distance travelled by light in a year.

Micron : All other are units of weight, this is of length

milligram: All other are units of , this is of weight