To determine:Name the variables, specify for each variable whether it should be treated as categorical or quantitative and give the units for quantitative variables, if available. 

Given info:
The data is collected by the students of an upstate New York college for their ecology class. Several biological, physical, and chemical variables were recorded, including stream name, substrate of the stream (limestone, shale or mixed), acidity of water (pH), temperature (@C) and BCI (measure of biological diversity).
Justification:
The variables considered in the study are stream name, substrate of the stream (limestone, shale or mixed), acidity of water (pH), temperature (°C) and BCI (measure of biological diversity).
Categorical variable:
Categorical variable categorizeseach individual to corresponding groups. It is used for the classification of individuals based on some attributes or qualities or characteristics. Categorical variable is also called as qualitative variable or nominal variable.
Quantitative variable:
A variable that provides numerical values of individual and arithmetic operations such as addition and subtraction that produce meaningful results are called quantitative variables. It
contains measured numerical values with measurement units.
Thestream name and substrate of the stream (limestone, shale or mixed) categorize the streams, which do not take natural numerical values. Even if some numerical values are assigned to these variables, arithmetic operations on such values are meaningless. Thus, the variables stream name and substrate of the stream (limestone, shale or mixed) are categorical.
The acidity of water (pH), temperature (@C) and BCI (measure of biological diversity) take natural numerical values, the addition and subtraction of which produce meaningful results. Thus, thevariables acidity of water (pH), temperature (@C) and BCI (measure of biological diversity) are quantitative.
The unit of acidity of water is pH. The unit of temperatures (@C), The unit of BCI is not specified.