the radioactive isotope europium decays with a first order rate constant of 0.062 year-1. What fraction of the europium in a sample is still present 55.0 years later

If soap hits the floor, is the soap dirty or the floor

Compare and contrast physical changes with chemical changes.

This chart lists four kinds of polymers and their sources. what can be known about all four polymers, despite their differences? they come from living things. they share ionic carbon bonds. they are at least 100 monomers long. they are made of repeating subunits.