Final answer:
The transition metals are known for the belated filling of their next-to-outermost energy level, where the d-orbitals are filled after the s-orbital of the valence shell. They display a wide range of oxidation states and properties due to their electron configuration.
Step-by-step explanation:
The family of elements known for the belated filling of their next-to-outermost energy level is the transition metals (c). This characteristic is due to their unique electron configuration where the d-orbitals of the penultimate shell (next-to-outermost energy level) get filled with electrons after the s-orbital of the valence shell has already been filled.
To address the different parts of this question regarding the periodic table:
- The alkali metals belong to Group 1.
- The halogens are located in Group 17.
- The noble gases are found in Group 18 and their energy orbitals are full, making them very unreactive.
- Element with atomic number 12 is magnesium, an alkaline earth metal in Group 2.
- An element with four neutrons in its nucleus is helium, which is a noble gas.
- Elements containing electrons in the 4th energy level are found starting in period 4 of the periodic table.
For the specific groups mentioned:
- Krypton is a noble gas.
- Selenium is a chalcogen.
- Barium is an alkaline earth metal.
- Lithium is an alkali metal.