In a normal distribution what percent of values fall within one standard deviation of the mean?
19.1%
15%
30%
68.2%

Roughly 68% of the distribution is between z = -1 and z = +1, ie within 1 standard deviation of the mean. This is from the 68-95-99.7 rule or better known as the Empirical Rule. 

The final answer is choice D) 68.2%