Question

what is light year?what is it's unit?

Answer 1

The light-year is a unit of length used to express astronomical distances and measures about 9.46 trillion kilometres or 5.88 trillion miles. As defined by the International Astronomical Union, a light-year is the distance that light travels in vacuum in one Julian year. 

Answer 2

The distance travelled by light in one year is called light year.
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It's unit is 9.46 ×10 power 14 metres.
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hope it helps you