a mixture of gases is prepared for laboratory experiments by combining 4.2 L of oxygen, 0.71 L of nitrogen, and 0.22 L of carbon dioxide. Determine the percentage of nitrogen in the mixture.

All at the same pressure and temperature? It matters.

Now percentage by mass?
Percentage by number molecule?

I suppose you want precentage by mass, but am not certain.

PercentN2= massN2/total mass

So assume sTP, as long as all are the same temp pressure, it doesn't matter.

massN2=.71/22.4 * 28 grams
massO2=4.2/22.4 * 32 grams
massCO2=.22/22.4 *44 grams

add to get toral, then figure percent.

What kind of percent? volume percent, mass percent, ---

If you want volume percent, then
%N2 = (volume N2/total volume)*100 = ?

To determine the percentage of nitrogen in the mixture, we need to calculate the total volume of the mixture and then find the proportion of nitrogen in that volume.

To find the total volume of the mixture, we add up the individual volumes of the gases:

Total volume = Volume of oxygen + Volume of nitrogen + Volume of carbon dioxide
Total volume = 4.2 L + 0.71 L + 0.22 L
Total volume = 5.13 L

Now, to find the percentage of nitrogen in the mixture, we divide the volume of nitrogen by the total volume of the mixture and multiply the result by 100:

Percentage of nitrogen = (Volume of nitrogen / Total volume) × 100

Percentage of nitrogen = (0.71 L / 5.13 L) × 100
Percentage of nitrogen ≈ 13.84%

Therefore, the percentage of nitrogen in the mixture is approximately 13.84%.