Final answer:
The primary safety concern with ethanol is its flammability, making it very important to handle it away from flames and heat. It is also an irritant and an environmental hazard, but flammability is the primary concern. Option C is correct.
Step-by-step explanation:
The primary safety precaution / concern associated with ethanol is its flammability. Ethanol (also known as ethyl alcohol, grain alcohol, or alcohol) is a volatile, flammable, colorless liquid with a slight characteristic odor. It is commonly used in alcoholic beverages, as a solvent, and in personal care products such as rubbing alcohol.
When handling ethanol, it is critically important to keep it away from open flames and heat sources, as it can easily ignite. While ethanol is an irritant, and can be an environmental hazard if not disposed of properly, flammability is its most immediate safety concern. Additionally, ethanol should never be ingested in the form of rubbing alcohol or laboratory-grade solutions, as these can contain additives that make them toxic.
In the context of the provided options, the correct answer is C. 1, 4, which stands for irritant and flammable.