Final answer:
a.'The number and types of elements you picked for your compounds' In the activity, the test variable (independent variable) is likely to be as they form the basis of experimental design in creating multiple compounds.
Step-by-step explanation:
In the activity described, the test variable (independent variable) would typically be a. The number and types of elements you picked for your compounds. When creating multiple compounds, the choices you make regarding which elements to combine form the basis of your experimental design.
The types of compounds resulting from these choices (whether they are ionic, covalent, etc.) would generally be considered part of the outcome that you observe, making them dependent variables rather than independent variables.
Similarly, the number of atoms in each compound, although they are a result of the independent variable, mainly reflect the proportions and ratios inherent in the compound's formula and are not typically the focus of manipulation as an independent variable in a straightforward compound construction activity.