Why is human skin purple when uv light is shined on it?

All cells are made of four types of acids, lipids, proteins, and carbohydrates.

Mike and mitchell decide to have a foot race. they mark off a stretch of 100 yards, and recruit cindy to work the stopwatch. after running the race and looking at the results, cindy declared that mitchell was the fastest. so how did the boys times compare?

The molar mass of nickel(ni) is 58.7 g/mol. how many moles are in an 88 gram sample of nickel?