Water-reactive substances pose safety risk because they release what when in contact with water?

• A. A flammable or health-hazard gas
• B. Oxygen gas only
• C. Hydrogen gas only
• D. Water vapor

Answer: (A)

When water-reactive substances come into contact with water, they release a gas. That gas is the safety concern because it can be flammable or pose health hazards if inhaled. Hydrogen gas is a common product and is highly flammable, but some reactions can also emit other toxic gases depending on the substance. Oxygen gas or water vapor aren’t the typical hazards produced in these reactions, so the emphasis is on the gas that could ignite or harm people.