It emits high-intensity light and UV radiation harmful to the eyes.
Explanation
The burning of a magnesium ribbon in air is a classic example of a combination reaction (specifically oxidation), where magnesium reacts with oxygen to form magnesium oxide ($2Mg + O_2 \rightarrow 2MgO$). This reaction is highly exothermic and produces distinct physical observations.
Detailed Analysis:
- It releases toxic fumes that cause respiratory distress. is Incorrect: While inhaling magnesium oxide fumes can be hazardous (potentially causing metal fume fever), the specific warning against staring addresses the risk to the eyes, not the respiratory system.
- It emits high-intensity light and UV radiation harmful to the eyes. is Correct: Magnesium burns with an extremely bright, dazzling white flame. This intense light emission includes significant levels of ultraviolet (UV) radiation. Staring at this flame without eye protection can cause temporary blindness or permanent damage to the retina.
- It undergoes violent combustion with explosive potential. is Incorrect: The reaction is vigorous but proceeds as a steady combustion rather than an explosion.
- It releases radioactive particulate matter. is Incorrect: Magnesium is a non-radioactive element; its combustion involves chemical changes, not nuclear decay.
Key Takeaway:
The combustion of magnesium is characterized by a dazzling white flame that emits high-intensity light and UV radiation, necessitating the use of eye protection to prevent retinal damage.