Standardized tests for certain subjects, given to high school students, are scored on a scale of 1 to 5. Let X represent the score on a randomly selected exam. The distribution of scores for one subject’s standardized test is given in the table. A 2-column table with 5 rows. Column 1 is labeled score with entries 1, 2, 3, 4, 5. Column 2 is labeled probability with entries 0.18, 0.20, 0.26, 0.21, 0.15.

What is the standard deviation of the distribution?

1.3
1.6
1.7
2.5