Which of the following properties refers to the colored powder resulting from rubbing a mineral against a harder surface?
f hardness
g luster
h streak
j cleavage

Streak is the correct answer.

Explanation:

In mineralogy, streak refers to color of the powder that results from dragging a mineral across a harder surface. The line usually has a more consistent color than the one from the mineral itself; this characteristic is very important to identify the mineral.

.) the observation by semmelweis that more mothers died of childbed fever when their doctors also worked in the morgue

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.