Science (086) — AI-generated practice question

(a) The ozone layer is a region in the upper atmosphere (stratosphere) where ozone (O₃) is present in higher concentrations. It shields Earth's surface from harmful ultraviolet (UV) radiation from the Sun.

(b) UV radiation splits O₂ molecules into free oxygen atoms, which then combine with O₂ to form ozone:

$$O_2 \xrightarrow{\text{UV}} O + O$$
$$O + O_2 \rightarrow O_3 \text{ (Ozone)}$$

(c) Synthetic chemicals called chlorofluorocarbons (CFCs), used in refrigerants and fire extinguishers, have caused ozone depletion, which began to drop sharply in the 1980s. Consequences include increased UV radiation reaching Earth's surface, which is highly damaging to organisms — for example, it causes skin cancer in human beings.

(d) In 1987, the United Nations Environment Programme (UNEP) forged an agreement to freeze CFC production at 1986 levels. It is now mandatory for all manufacturing companies worldwide to produce CFC-free refrigerators.

Source: Chapter 13, Section 13.2.1

---

• The question has four sub-parts, so answer all four clearly labelled — examiners check this.
• Include both chemical equations for part (b); writing only one loses marks.
• For part (c), name CFCs specifically and give at least one consequence (skin cancer).
• For part (d), mention the year (1987), UNEP, and the CFC-free refrigerator mandate — these are the specific facts examiners look for.
• Keep language concise; do not repeat information across sub-parts.