Environmental Chemistry

Step 1: PCB’s are well known environmental carcinogens.
Step 2: Tetrachloroethene (perchloroethylene) is also suspected carcinogenic solvent.
Step 3: Sodium chlorate is an oxidizer but not carcinogenic. Hence → (D).

Step 1: Recall the octet rule. The octet rule states that atoms tend to combine in such a way that they have eight electrons in their valence shell. Step 2: Examine each molecule.

CO : Carbon forms two double bonds with oxygen. Carbon and oxygen both complete their octets. ✔
H S: Sulphur has eight electrons around it (two bonding pairs and two lone pairs). ✔
NH : Nitrogen has three bonding pairs and one lone pair, completing its octet. ✔
BF : Boron forms three bonds and has only six electrons in its valence shell, not eight. ✘
Step 3: Final conclusion. The octet rule is not satisfied in BF .