Alveoli. I don't know what a nephron is but neurons and synapses are in the brain.
The valves stop the blood from flowing backwards
Answer:- 0.134 seconds
Solution:- The speed is given as 
and the circumference is 24900 miles which is same as the distance light have to covered. It asks to calculate the time required to cover this distance by the light.
We need to do unit conversion from miles to meter as the speed is given in meter per second.
1 mile = 1609.34 meter
So, 
= 40072566 meters
Know that, 
It's rearranged to time as, 
Let's plug in the values in it:
= 0.134 seconds
So, the light would take 0.134 seconds to travel the mentioned speed. The answer without the unit is 0.134.
Excuse me not giving an explanation; I haven't even learned chemistry before. I usually give explanations for math/english.
I think it would be for flourine: 7
aluminum: 8
can't help with the rest...
sorry!
Answer:
nitric acid + iron=iron+[nitric acid ] 2 hydrogen
