Answer :
Answer: option B
Explanation:
The number of valence electrons in an atom determines its chemical properties and how it will bond with other atoms.
For monoatomic elements, they typically exist as individual atoms and their valence electrons are involved in bonding. However, for some elements, it's not energetically favorable for them to exist in monoatomic form due to their electron configurations.
Given the information provided:
- Element X has 2 valence electrons in its outer shell.
- Element Y has 8 valence electrons in its outer shell.
- Element Z has 6 valence electrons in its outer shell.
Looking at the periodic table, we can identify these elements:
- Element X with 2 valence electrons in its outer shell is likely Helium (He).
- Element Y with 8 valence electrons in its outer shell is likely Neon (Ne).
- Element Z with 6 valence electrons in its outer shell is likely Carbon (C).
Among these elements, Helium (He) and Neon (Ne) are noble gases, which exist as monoatomic gases under normal conditions. However, Carbon (C) typically forms covalent bonds and exists in various molecular or network structures (like diamond or graphite) rather than as individual atoms.
So, the element that doesn't exist in the monoatomic state is Element Z, which is Carbon (C). Therefore, the correct answer is:
b. Z
