Percentage of nitrogen in clean dry air

78.1 percent

Explanation:

Nitrogen is far and away the most common gas in our atmosphere. It makes up 78.1 percent of clean (as IF), dry air by volume (since nitrogen is a fairly light molecule, it makes up about 75.5 percent of the mass of the atmosphere)

for step 7 table c on the lab "newtons law of action"   the average time it took the car to travel .25 meters   was 1.92 seconds.

the average time it took the car to travel 0.50 meters was 2.61 seconds

hope this : )