Considering the definition of percentage by mass, the sample of pure lithium nitrate contains 7.99% lithium by mass.
<h3>Definition of percentage by mass</h3>
The percentage by mass expresses the concentration and indicates the amount of mass of solute present in 100 grams of solution.
In other words, the percentage by mass of a component of the solution is defined as the ratio of the mass of the solute to the mass of the solution, expressed as a percentage.
The percentage by mass is calculated as the mass of the solute divided by the mass of the solution, the result of which is multiplied by 100 to give a percentage. This is:

<h3>This case</h3>
Because percent by mass indicates the ratio of solute to solution based on mass, if the sample has twice the mass of the first sample, the ratio remains constant.
So the percentage by mass is the same.
That is, the sample of pure lithium nitrate contains 7.99% lithium by mass.
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Learn more about percent by mass:
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The only reaction that will most likely take place based on the activity series is; C: Ba + Na₂CO₃
<h3>Activity Series</h3>
From the activity series given, we can say that during a displacement reaction, the more reactive metal will always displace the lesser reactive metal from a compound.
Let us look at each of the given options;
A) Ag + FeCl₃
From the activity series, Silver(Ag) is less reactive than Iron(Fe) and as such Silver cannot displace iron from its' compound.
B) Zn + CaO
Zinc (Zn) is a less reactive metal than Calcium (Ca), so it cannot cannot displace Calcium from its' compound.
C) Ba + Na₂CO₃
Barium (Ba) is a more reactive metal than Sodium (Na), and therefore Barium will displace sodium from its compound in a displacement reaction.
D) Cr + KNO₃
Chromium (Cr) is a lesser reactive metal than Potassium (K), and it therefore cannot displace Potassium from its compound.
Complete question is;
Which reaction will most likely take place based on the activity series? Li > K Ba > CaNa > Mn > Zn > Cr> Fe> Cd Ni > H > Sb > Cu > Ag > Pd > Hg > Pt
A. Ag + FeCl₃
B. Zn + CaO
C. Ba + Na₂CO₃
D. Cr + KNO₃
Read more about Activity Series at; brainly.com/question/17469010
I would say C is the answer for this one.