Copper has two isotopes. The Cu-63 isotope weighs 62.9296 amu and has 69.17% of the natural abundance. What is the atomic mass (in amu) of the second copper isotope if the average atomic mass of copper is 63.546 amu?

The nucleus of ⁶Li is a powerful absorber of neutrons. It exists in the naturally occurring metal to the extent of 7.5%. In the era of nuclear deterrence, large quantities of lithium were processed to remove 6Li for use in hydrogen bomb production. The lithium metal remaining after removal of ⁶Li was sold on the market. (a) What are the compositions of the nuclei of ⁶Li and ⁷Li?