Natural events like volcanoes contribute to atmospheric chlorine.

• A. They contribute but are not the main source
• B. They are the main source
• C. They do not contribute
• D. They remove chlorine

Answer: (A)

Volcanoes do release chlorine compounds, so natural events do contribute to atmospheric chlorine. But they are not the main source. The majority of chlorine in the atmosphere that affects ozone comes from human-made products like chlorofluorocarbons and halons that release chlorine when they break down in the upper atmosphere. Volcanic chlorine is episodic and localized, so its global impact is smaller compared to these anthropogenic sources. That’s why the statement that natural events contribute but are not the main source is the best fit. The other options overstate or misstate the role: they don’t reflect that natural sources exist but are not dominant, and they don’t describe removal of chlorine.