1. An atom of ⁶⁵Zn⁺² would contain how many neutrons, protons, and electrons?

2. 21.37 or A wooden artifact from a Chinese cave has a ¹⁴ C activity of 7.9 counts per minute as compared with an activity of 31.7 counts per minute for a standard of zero age. From the half life for ¹⁴ C decay of 5.7x10³ years, determine the age of the artifact.

3. The half life for the decay of Th 232 is 1.39x 10¹⁰ years. If the earth formed 4.5x10⁹ years ago, how much of the original Th 232 present at its formation is still present?

4. 21.39 or A uranium mineral that originally crystallized with no Pb present, now contains 11.0 mg of 206 Pb for each 50 mg of 238 U. The half life of decay for the process 238 U = 206 Pb is 4.5 billion years.

a) To calculate the age of the mineral, the geologist set Ao = 50 + 11(238/206) and A_t =50. Why do they do that?

b) What is the age of the mineral?

5. Based on their positions in the periodic table, select the atom with the largest radius. a) Al b) P c) Si d) Ga e) Ge

6. 21.40