The Mann-Whitney U test is a non-parametric alternative to the student's t- test and measures the likelihood that a randomly selected value from sample set 1 will be significantly different from a randomly selected value from sample set 2. When testing for a significant lowering in the value of a parameter in sample set 2, the U test counts the total number of occasions for which any value in set 2 is higher than any value in set 1. The null hypothesis can be rejected if the calculated U value so derived is less than or equal to a test statistic. Use the Mann-Whitney U test to determine if protein precipitation has significantly reduced the concentration of Mg* ions in six independent samples of human blood plasma (see the data in Table 1 below and then answer all four questions a) to d)). Table 1 Concentration of Mg in ug/ml in human plasma prior to protein precipitation Concentration of Mg* in ug/ml in in human plasma after protein precipitation 10.0 9.0 9.4 7.0 7.7 6.4 8.3 8.0 9.6 6.2 10.2 7.6 а) What are the benefits of using a non-parametric test such as the Mann- Whitney U test relative to a parametric test such as the student's t- test? b) What is the null hypothesis for the protein precipitation treatment experiment?