Physical change. Physical changes are changes affecting the form of a chemical substance, but not its chemical composition. ... Physical changes occur when objects or substances undergo a change that does not change their chemical composition.
27) mechanical weathering
28) overgrowth of algae that produce toxins
29) Weathering breaks down and loosens the surface minerals of rock so they can be transported away by agents of erosion such as water, wind and ice. There are two types of weathering:mechanical and chemical. Mechanical weathering is the disintegration of rock into smaller and smaller fragments.
30) I'M NOT SURE
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Answer:chlorofluorocarbons (CFCs)
halon.
carbon tetrachloride (CCl4)
methyl chloroform (CH3CCl3)
hydrobromofluorocarbons (HBFCs)
hydrochlorofluorocarbons (HCFCs)
methyl bromide (CH3Br)
bromochloromethane (CH2BrCl)
Explanation:
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Answer : We can produce 125.7 g of
.
Explanation : The reaction will be

The molecular mass of
is 64.1 g/mol
and molecular mass of
is 34.1 g/mol
For every mole of
we would need twice of
moles, so for every 3 moles of
we need 16 moles of 
Now, we can calculate number of moles
2.61 X (3/16) = 0.49 moles
Here, the molecular mass of
is 256.8 g
multiplying it with the number of 0.49 moles we get, 256.8 X 0.49 = 125.7 g of
.
Hence, 125.7 g of
will be produced.