Answer: Option (d) is the correct answer.
Explanation:
When an element has incompletely filled valence or outermost shell then that atom is most likely to undergo a chemical reaction in order to attain stability.
For example, sodium has atomic number 11 and its electronic configuration is 2, 8, 1. So, to attain stability sodium will readily loose 1 electron. Hence, it will become reactive in nature to attain stability.
Whereas argon has atomic number 18 and its electronic configuration is 2, 8, 8. Therefore, its valence shell is completely filled so, it will not react easily.
Hence, we can conclude that family of group 18 on the periodic table is least likely to enter into chemical reactions.