Explanation:
The lines in the spectra of star is due to absorption of light emitted by star by different elements present in atmosphere of the star .
If some element is present in the outer atmosphere of he star , it will absorb a particular portion of light , for which there will be black line in the spectrum .
These are called Fraunhoffer's lines .
Now there is no such line at the place of Helium in the light spectrum . This means that Helium element is not present in the outer atmosphere of the star.
Answer:
Oxygen cycle
Explanation:
The components of the reservoirs of oxygen that are exchange in our environment is the oxygen cycle
It suggests the movement of oxygen between the living and non-living parts.
- The cycle does not account for oxygen that is trapped and cannot be exchanged in nature.
- Oxygen is important component of the atmosphere.
- Gaseous exchange between living organisms and atmosphere involves oxygen to a very large extent.
Answer:

Explanation:
Temperature of the house, 
Convert to rankine, 
Heat is extracted at 40°F i.e 
Calculate the coefficient of performance of the heat pump, COP

The minimum power required to run the heat pump is given by the formula:
...............(*)
Where the heat losses from the house, 
Substituting these values into * above

Answer: 529.9 Hz
Explanation:
Here we need to use the Doppler equation, so we have:
f' = f*(v + v0)/(v - vs)
Here, f is the frequency = 500Hz
v is the velocity of the wave, = 334m/s
v0 is the velocity of the observer = 20m/s
vs is the velocity of the source = 0m/s
Then we have:
f' = 500Hz*(334m/s + 20m/s)/(334m/s) = 529.9 Hz
Motion is the correct word that fits in.
Hope this helps.