Answer:
a. BH₃
Explanation:
According to the octet rules, atoms reach stability when are surrounded by eight electrons in their valence shell when they combine to form a chemical compound.
From the options, the only compound in which the central atom does not meet the octet rules is BH₃. The central atom is boron (B), which has 3 electrons in its valence shell. When B is combined with hydrogen (H), 3 electrons from the 3 atoms of H are added. The total amount of electrons is 6, fewer than 8 electrons needed to meet the rule.
The compound which is showing exception to the octet rules is BH₃.
According to the octet rule in the outermost valence shell of any compound, eight electrons should present.
Among the given compounds only BH₃ will not satisfy the octet rule, as in the outermost shell of boron atom 3 electron are present following the electronic configuration 1s²,2s²2p¹ because its atomic number is 5. Now this boron atom will form bond with 3 hydrogen atoms and these hydrogen atoms will share 3 electrons to boron atom.
So, total electrons in the outer most shell of BH₃ compound is 3+3=6.
Hence, BH₃ is an exception of octet rule.
To know more about octet rule, visit the below link:
https://brainly.com/question/7620705
