Answer
The same number of particles in a gas spread further apart than in the liquid or solid states.
Explanation:
The same number of particles in a gas spread further apart than in the liquid or solid states. The same mass takes up a bigger volume. This means the gas is less dense. Density also depends on the material.
To solve this problem we will apply the concepts related to the principle of destructive and constructive interference. Mathematically this expression can be given as

Here,
n = Index of refraction
t = Thickness
m = Order of the reflection
= Wavelength
We have all of this values, therefore replacing,

Therefore the thickness of the oil slick is 233nm
We are given that a 500 kg object is hanging from a spring. To determine the amount the spring is stretched we will use Hook's law, which states the following:

Where:

Since the object is hanging the only force acting on the spring is the weight of the object. The weight of the object is:

Where:

Plugging in the values we get:

Solving the operations:

Now we solve for "x" from Hook's law by dividing both sides by "k":

Now we plug in the known values:

Solving the operations:

Therefore, the spring is stretched by 5.4 meters.
Answer:
c. index fossil
Explanation:
Trilobite fossils are found worldwide, with many thousands of known species. Because they evolved rapidly, and molted like other arthropods, trilobites serve as excellent index fossils. (Arthropods periodically shed their old exoskeletons, or molt.) An index fossil is one that is useful for dating and correlating the strata in which it is found.