Independent Variable: a variable that you can change in an experiment
Dependent Variable: something that changes as you change the independent variable
control variable: something that is not changed throughout the experiment
Answer:
a) 
b) 
c) 
Explanation:
Hello,
a) In this case, the given height in cm is:

And the radius in cm is:

Thus, the volume in cubic centimeters which is also equal in mL (1cm³=mL) is:

b) In this case, the given height in mm is:

And the radius in mm is:

Thus, the volume in cubic millimeters is:

c) Finally, since 1000 mL equal 1 L, the required density in g/L turns out:

Best regards.
Because its only representing the most stable isotope of that element but its considered the atomic mass and not average atomic mass