Emissions of sulphur dioxide by industry set off chemical changes in the atmosphere that result in acid rain. The acidity of liquids is measured by pH on a scale from 0 to 14. Distilled water has pH of 7.0 and lower pH values indicate acidity. Theory suggests that the pH of rain varies among rainy days according to a normal distribution with mean 5.4 and standard deviation 0.5. The random sample of 21 days gives a sample standard deviation 0.8. You would like to test if the population standard deviation is indeed 0.5 as the theory suggests. At significance level 5 per cent, that is, x=0.05, what is the test statistic and what are the critical values?

Test statistic: 51.2. Critical values: 9.591 and 34.170.

Test statistic: 25.6. Critical values: 10.283 and 35.479.

Test statistic: 53.76. Critical values: 10.283 and 35.479.

Test statistic: 25.6. Critical values: 9.591 and 34.170.