Answer:
The dolphins average speed is 3.51 
Explanation:
First of all, the following rules of three should be applied:
- If 1 mile is equal to 1609 meters, 20 miles are equal to how many meters?

distance=32,180 meters
- If 1 minute is equal to 60 seconds, 153 minutes is equal to how many seconds?

time= 9,180 seconds
Speed is a physical quantity that expresses the relationship between the space traveled by an object and the time used for it. That is, speed implies the change of position of an object in space within a certain amount of time and is calculated as:

So in this case the velocity is calculated as:

Solving, you get:
Speed= 3.51 
<u><em>The dolphins average speed is 3.51 </em></u>
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Answer: there is none, there is no group six period 2 as far as i know .
Explanation:look up the periodic table
Answer:
n = 5 to n = 6 absorption
n = 9 to n = 6 emission
n = 6 to n = 4 emission
n = 6 to n = 7 absorption
Explanation:
According to the Bohr's model of the atom. An electron in an atom may absorb energy and move from a lower energy level to a higher energy level. This requires absorption of energy that is equal to the energy difference between the two levels.
Similarly, an electron may move from a higher to a lower energy level, releasing energy that is equal to the energy difference between the higher and the lower level. This is known as emission.
Hence, if the electron is moving from a lower energy level to a higher energy level, an absorption has taken place, e.g n = 5 to n = 6
When an electron moves from a higher energy level to a lower energy level, an emission has taken place e.g n = 9 to n = 6