To measure the concentration of an aqueous solution of , an analytical chemist adds strong acid to a sample of the solution and titrates it to the endpoint with of potassium permanganate solution. The balanced chemical equation for the reaction is:

The question is incomplete, the complete question is shown in the image attached.

7.69%

Explanation:

The balanced equation of this reaction is shown in the image attached to this answer.

The reaction is redox because we can notice a change in the oxidation number of species from left to right in the reaction equation.

For instance, the oxidation number of oxygen was changed from -1 in H2O2 to zero in O2. Hence H2O2 was oxidized.

To calculate the percentage of H2O2 in the sample;

number of moles of KMnO4 =  137 ml/1000 * 0.230 M = 0.03151 moles of KMnO4

From the reaction equation;

2 moles of permanganate reacts with 5 moles of H2O2

0.03151 moles of permanganate reacts with  0.03151 moles * 5/2 = 0.079 moles of H202

Mass of H2O2 reacted = 0.079 moles of H202 * 34 gmol-1 = 2.69 g

Hence % by mass of H2O2 in the sample = 2.69 g/35 g * 100 = 7.69%

the answer is na (sodium)