Answer: c
Explanation:
during the industrial revolution americans were switching from rural to urban life, thus using up more fossil fuels, and working in factories
Answer:
morlecular element is oxygen
Answer:
: Pure substance, Element
: Pure substance , Element
: Pure substance, Compound
Explanation:
Element is a pure substance which is composed of atoms of similar elements.It can not be decomposed into simpler constituents using chemical reactions.Example:
and 
Compound is a pure substance which is made from atoms of different elements combined together in a fixed ratio by mass.It can be decomposed into simpler constituents using chemical reactions. Example: 
Heterogeneous Mixture : Mixture that has its different components mixed unevenly within the substance
. Example: Air
Homogeneous Mixture : Mixture that has its different components mixed evenly within the substance. Example: sugar dissolved in water
Water is H2O, whereas Hydrogen Peroxide is H2O2 -> the extra oxygen atom changes the substance entirely.