Final answer:
The chemical class known for having antimicrobial effects in extremely small amounts is heavy metals, which are oligodynamic. Among the provided options, antibiotics are the correct answer as they are potent antimicrobial agents effective in low doses.
Step-by-step explanation:
The property of having antimicrobial effects in exceedingly small amounts is characteristic of heavy metals. These are known for their oligodynamic activity, meaning they exhibit significant antimicrobial activity even at low concentrations. Heavy metals like silver and copper are used in various forms in antiseptics and disinfectants. When heavy metal ions bind to proteins, particularly sulfur-containing amino acids, they inhibit enzymatic activity and denature the proteins, leading to the death or inhibition of the microorganism.
While heavy metals are not explicitly listed in the question's answer options, they align closely with the concept described. However, if we're strictly considering the options provided: antibiotics (a), antiseptics (b), disinfectants (c), and steroids (d), the correct answer would be antibiotics. Antibiotics are chemical compounds that can have potent antimicrobial effects in relatively low doses. They are designed to target specific microbial structures and enzymes, killing or inhibiting microorganisms with few effects on the host.