Answer:
-2
Explanation:
Calcium is the element of second group and forth period. The electronic configuration of Calcium is - 2, 8, 8, 2 or 
There are 2 valence electrons of Calcium.
Thus, calcium loses two electrons to sulfate ion and sulfate ion accepts these electrons to form ionic bond.
Calcium sulfate, 
is formed when 2 valence electrons of calcium are loosed and they are gained by sulfate ion.
Thus, the charge on the sulfate ion is -2.
I believe the correct answer from the choices listed above is option D. An object is seen to either speed up, slow down, or change direction due to <span>unbalanced forces. When a system is subjected to unbalanced forces, the object would tend to move or change in motion. Hope this answers the question.</span>
12 times breathe give 240 ml of pure 
. Each breathe gives 20 ml of .
Let us consider, volume of air per breathe= x ml.
Pure from inhaled air= 
ml and Pure from exhaled air= 
ml.
Pure from inhaled and exhaled air= 20 ml
So, + = 20
Therefore, x = 55.5 ml
So, volume of air per breath= 55.5 ml.
Answer:
independent variable -- different batteries
dependent variable -- the time that clock stop
Explanation:
In an experiment or a research study, there are two type of variables that can affect the result of the experiment or the conclusion. They are independent variable and the dependent variable.
An independent variable may be defined as that variable in an experiment which can be changed or can be controlled in the scientific experiment in order to test the effect on the dependent variable. It cannot be changed by other variables.
On the other hand, dependent variable are those are those which can be altered or change that can affect the experiment.
In the context, Emily uses the different types of the batteries as an independent variable and the time where the clock stopped in the dependent variable in her research.
