B .combustion because HOH and CO2 are the products of complete combustion
Answer:
NO3-
Explanation:
Given the reaction equation;
Au(s) + 3NO3-(aq) + 6H+(aq)→Au3+(aq) + 3NO2(g) + 3H2O (l).
We can consider the oxidation states of species on the left and right hand sides of the reaction equation;
Au is in zero oxidation state on the left hand side and an oxidation state of +3 on the righthand side.
NO3- is in oxidation state of +5 on the righthand side and NO2 is in + 4 oxidation state.
H+ is in + 1 oxidation state on both the left and right hand sides of the reaction equation.
Since reduction has to do with a decrease in oxidation number, it follows that NO3- was reduced in the reaction.
You need to multiply 15 by 2 since each student is doing 2 trials which gives you 30 (you can think of it as 30 students doing it once if that helps you). Then you have to multiply 30 by 50 since the experiment is being done 30 times and each time requires 50mL which equals 1500mL.
Therefore the teacher needs to make 1500mL of solution for the lab.
I hope this helps.