Question

A class was performing an experiment to discover the pH values of some common household substances. The results of three groups are shown in the table below.
Substance
Group 1 pH
Group 2 pH
Group 3 pH
Lemon juice
2.2
2.2
2.1
Vinegar
2.8
2.8
8.2
Baking soda
8.4
8.5
8.4
Milk of magnesia
10.2
10.3
10.2

Which statement best describes evidence that Group 3’s data are less valid than the data for the other two groups?
Group 3’s pH value for lemon juice is lower than the values of the other two groups.
Group 3’s pH value for vinegar is much higher than the values of the other two groups.
Group 3’s pH value for baking soda does not exactly match the values of the other two groups.
Group 3’s pH value for milk of magnesia is different from the value obtained by Group 2.

Answer 1

Validity is the extent to which a measurement is corresponds to the real or actual value.
So "Group 3’s pH value for vinegar is much higher than the values of the other two groups." is the answer since 8.2 is so far from 2.8 which the other two groups got and seems to be valid.

Answer 2

The statement, which best describes the evidence that Group 3’s data are less valid than the data for the other two groups is this: GROUP 3’S pH VALUE FOR VINEGAR IS MUCH HIGHER THAN THE VALUES OF THE OTHER TWO GROUPS.

An experimental result is said to be valid, if it gives the true values of the parameters it has measure. Looking at the experimental results given in the question above, one will notice that, the pH value obtained by group 3 for vinegar is quite different from that of the other two groups. In addition, the value is wrong, this is because, vinegar is acidic in nature. The result obtained by group 3 indicates that vinegar is basic, which is wrong. This shows that the results obtained by group 3 is less valid than that of the other two groups.