Answer:
a) HCl
Step-by-step explanation:
As we know, that HCl or Hydrogen Chloride is a diatomic compound. It is formed due to the Chemical reaction of Hydrogen and Chlorine. As both Hydrogen and Chlorine have valencies of 1, the Net Valency of the Compound HCl is 1 itself. This separates it from the rest of the compounds. The rest of the compounds need to have more than 2 atoms of each kind and have different valencies too.