ellen has a 40 g sample of nitrogen-13. the half-life of nitrogen-13 is 10 minutes. what is the mass of nitrogen-13 in ellen’s sample after 30 minutes?

Write the symbol for every chemical element that has atomic number greater than 3 and atomic mass less than 12.0 u.

Working with si (metric) units for each of the following commonly used measurements, indicate its symbol. liter gram milliliter kilogram meter centigram milligram centimeter kilometer second millimeter milliseconds

How can carbon move from "land" to bodies of water? describe the way human impact has lead to increased levels of co2 in the atmosphere.