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Answer #1:

Physical.

Explanation:

The only thing mentioned to change is the color. Nothing about the gas in general is changing

Answer #2:

Chemical.

Explanation:

The fact this interacted with another element to completely turn something else rather than just being that color makes this a chemical change.

Answer #3:

Physical

Explanation:

Well, how does an element's density have to do anything with a chemical change?

Answer #4:

Chemical.

Explanation:

Fire/heat is involved, and it makes it change states.

b mirrors submit a iisner? e. for which optical devices does d sometimes have a positive value? o a a and b o b. a and c o c. b and d 0 d. b and cb

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.