### Question
How is the "class II substance" defined?


### Answer
The term **class II substance** is defined in *42 U.S.C. § 7671* as follows -

> each of the substances listed as provided in section 7671a(b) of this title

#### Citation:
  - *42 U.S.C. § 7671*
  - Heading: **CHAPTER 85-AIR POLLUTION PREVENTION AND CONTROL > SUBCHAPTER VI-STRATOSPHERIC OZONE PROTECTION**

