Answer: a. The electron configuration for sodium (atomic number 11) is:
1s² 2s² 2p⁶ 3s¹
b. The electron configuration for iodine (atomic number 53) is:
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹0 4p⁶ 5s² 4d¹0 5p⁵
c. The electron configuration for iron (atomic number 26) is:
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶