Question

which one of the following violates the octet rule?
a nf₃
b asf₅
c cbr₄
d pcl₃

Explanation:

Step1: Analyze \( NF_3 \)

Nitrogen (\( N \)) has 5 valence electrons. In \( NF_3 \), it forms 3 single bonds with fluorine (\( F \)) atoms. Each \( F \) has 7 valence electrons and forms 1 bond. Nitrogen has 3 bonding pairs and 1 lone pair (\( 3 + 1=4 \) electron pairs around \( N \)), and each atom ( \( N \) and \( F \)) has an octet.

Step2: Analyze \( AsF_5 \)

Arsenic (\( As \)) is in the same group as \( N \) but in a lower period. \( As \) has 5 valence electrons. In \( AsF_5 \), it forms 5 single bonds with \( F \) atoms. \( As \) has 5 bonding pairs (10 electrons around \( As \)), which violates the octet rule (octet rule is 8 - electron rule for main - group elements in most cases, and \( As \) here has an expanded octet).

Step3: Analyze \( CBr_4 \)

Carbon (\( C \)) has 4 valence electrons. In \( CBr_4 \), it forms 4 single bonds with bromine (\( Br \)) atoms. Each \( Br \) has 7 valence electrons and forms 1 bond. Carbon has 4 bonding pairs (8 electrons around \( C \)), and each \( Br \) also has an octet.

Step4: Analyze \( PCl_3 \)

Phosphorus (\( P \)) has 5 valence electrons. In \( PCl_3 \), it forms 3 single bonds with chlorine (\( Cl \)) atoms. Phosphorus has 3 bonding pairs and 1 lone pair (\( 3 + 1 = 4 \) electron pairs around \( P \)), and each atom (\( P \) and \( Cl \)) has an octet.

Answer:

B. \( AsF_5 \)