Which of the following definitions describes a chemical hazard?
a. can be present in dust, fumes, liquids, solids, mists, vapors, or gases of products used at a site or released during a construction job
b. microorganisms, such as bacteria, fungus, mold, or viruses that can cause illness
c. the most commonly thought of hazards for construction
d. these hazards can lead to injuries to the joints or muscles by way of heavy, frequent lifting, repetitive tasks

a. Can be present in dust, fumes, liquids, solids, mists, vapors, or gases of products used at a site or released during a construction job

Explanation:

Chemical hazard is a hazard caused by exposition to chemical dangers in the work place, chemicals can cause damage to humans and animals because they can be present in dust, fumes, liquids solids, mists vapors or gases, and they are difficult to detect, that is why they are very dangerous since they are really hard to detect.

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.