The four natural isotopes of iron have atomic masses of 53.9, 55.9, 56.9, and 57.9. If these were the only isotopes of iron and they occurred in equal abundance, which would be closest to the atomic mass of iron? A. 54
B. 55
C. 56
D. 57

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Which type of substance ionizes partially and gives off hydrogen ions when dissolved in water? a. strong acid b. strong base c. weak acid d. weak base

What are the first two quantum numbers for the electrons located in subshell 4d? what are the first three quantum numbers for the electrons located in subshell 2s? how many electrons can be held in a sublevel l = 3? how many electrons can be held in the energy level n = 4? how many electrons in an atom can share the quantum numbers n = 4 and l = 3?