I believe your answer would be B.
Answer:

Explanation:
¡Hola!
En este caso, teniendo en cuenta la información dada por el problema, inferimos que primero se debe usar la ecuación del gas ideal con el fin de calcular las moles de gas que se encuentran al inicio del experimento:

Seguidamente, usamos la ley de Avogadro para calcular las moles finales, teniendo el cuenta que el volumen final es el doble del inicial (8.50 L):

Quiere decir que las moles de N2(g) que se agregaron son:

¡Saludos!
It is moldm^-3s^-1
^ means raise to power
Let's divide the three experiments: The experiment with 10.00 mL of water is A), the experiment with 15.00 mL is B), and the experiment with 25.00 mL is C).
- (1) Now let's calculate the experimental density of each experiment. Density (ρ) is equal to the mass divided by the volume, thus:

- (2)To calculate the average density, we add each density and divide the result by the number of experiments (in this case 3):

- (3) The percent error is calculated by dividing the absolute value of the substraction of the theorethical and experimental values, by the theoretical value, times 100:
%error=
%error=
%error=2.44 %
Most definitely gravity. Gravity is what makes things go up and or down