Any of two or more forms of the same element which differ only in the number of neutrons their atoms contain is called an:
a. irregularity
b. isomer
c. isotope
d. irritability

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?