Question

The central atom in _____ violates the octet rule. Given the atomic number of
$Se=34$, $As=33$, $B=5$ and $N=7$.

• A. $N{H}_3$
• B. $Se{F}_2$
• C. $B{F}_3$
• D. $As{F}_3$

Answer 1

The correct option is C $B{F}_3$

The lewis dot structure of:
$N{H}_3$ is


$Se{F}_2$ is


$B{F}_3$ is

$As{F}_3$ is

The central atom $N,Se,As$ in $N{H}_{3}Se{F}_2$ and $As{F}_3$ have 8 valence electrons. But in case of $B{F}_3$, boron has an incomplete octet of only 6 electrons in its valence shell and hence violates the octet rule.