What is the half-life of an isotope if 125 g of a 500 g sample of the isotope remains after 3.0 years?
a.) 3.5 years
b.) 4.5 years
c.) 1.5 years
d.) 2.5 years

The comparison of the number of atoms in a copper coin the size of a penny with the number of people on earth is made to illustrate which of the following? a. that atoms are indivisible b. that atoms are very small c. that atoms are very large d. that in a copper penny, there is one atom for every person on earth

What does a complete balanced chemical equation include? a. exothermic coefficients b. endothermic coefficients c. valence electrons d. molar coefficients

How many atomic mass units are equal to 1.672×10−24 g of protons?