Final answer:
The correct critical value zα/2 for a 91% confidence level is found to be approximately 1.70, which corresponds to option A.
Step-by-step explanation:
The critical value zα/2 for a 91% confidence level can be found by understanding how the standard normal distribution works. A 91% confidence level means that the middle 91% of the distribution is within the critical values, leaving 9% to be split equally into the two tails of the distribution. This results in 4.5% in each tail. Therefore, the area to the left of the critical value is 1 - 0.045 or 0.955.
To find the corresponding z-score, one can use a z-table, calculator, or statistical software. The z-score associated with a cumulative area of 0.955 to the left is approximately 1.70. Thus, option A, with a value of 1.70, is the correct critical value zα/2 which corresponds to a 91% confidence level.