What law states that traits are passed from parents to offspring independently of one another

I believe the answer your looking for is a heredity law called Mendel's Law of independent assortment.

This is one of Mendel's principles that govern the process of genetic inheritance. It states that allele pairs separate independently during the formation of gametes (sex cells). This means that traits are passed to offspring independently of one another. The passing on of genetic traits from parents to offspring.