Answer:
29 L.
Explanation:
Hello!
In this case, considering that we are performing a conversion by which the time should be cancelled out to obtain liters, we first need to convert the seconds on bottom to hours and then the volume on top to liters, just a shown down below:

Which turns out 29 L with 2 significant figures.
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Answer:
There are 17.64% students received B+ grades.
Explanation:
It is given that,
Total number of students in chemistry class is 17
We need to find the percentage received by B+.
Number of students having B+ grades are 3 (from graph)
Required percentage = 
So, there are 17.64% students received B+ grades.
Answer:
2 elements magnesium(Mg) and chlorine (Cl)
I found the attached image with the same statement of your question and think it may be very useful for you that I use it to show how to answer this question (furthermore I think it may be the same reaction that you forgot to include).
As you can see, there are one image on the left side and other image on hte right side of the figure.
Those images contains drawings that represent molecules and a legend that permit you to distinguish the kind of atoms in each molecule.
Using that, you can indicate the chemical reaction as the transformation of the molecules on the left side onto the molecules on the right side:
Left side:
3 molecules of CH4 and 3 molecules of N2Cl4
Right side:
3 molecules of CCl4, 3 molecules of N2 and 6 molecules of H2
That is represented as:
3CH4 + 3 N2Cl4 -----> 3 CCl4 + 3N2 + 6H2And that is the balanced chemical equation for the reaction shown in the figured attached.I hope this is useful for you..