The speed of nitrogen molecules in the atmosphere (at 20ºc) follows a normal distribution with a mean speed of 500 meters/second and a standard deviation of 50 meters/second. this information best supports which conclusion?

a. 84% of the molecules have speeds between 450 meters/second and 550 meters/second.
b. 68% of the molecules have speeds between 450 meters/second and 550 meters/second.
c. 50% of the molecules have speeds between 450 meters/second and 550 meters/second.
d. 34% of the molecules have speeds greater than 550 meters/second.