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.

i look it up online and i'll tell you

  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-