I think it would be Bromine and Mercury, hope that helps
The answer I think it’s C I think.
Answer : The concentration of 
and 
are 
and 
respectively.
Solution : Given,
pH = 4.10
pH : pH is defined as the negative logarithm of hydronium ion concentration.
Formula used : ![pH=-log[H_3O^+]](https://tex.z-dn.net/?f=pH%3D-log%5BH_3O%5E%2B%5D)
First we have to calculate the hydronium ion concentration by using pH formula.
![4.10=-log[H_3O^+]](https://tex.z-dn.net/?f=4.10%3D-log%5BH_3O%5E%2B%5D)
![[H_3O^+]=antilog(-4.10)](https://tex.z-dn.net/?f=%5BH_3O%5E%2B%5D%3Dantilog%28-4.10%29)
![[H_3O^+]=7.94\times 10^{-5}](https://tex.z-dn.net/?f=%5BH_3O%5E%2B%5D%3D7.94%5Ctimes%2010%5E%7B-5%7D)
Now we have to calculate the pOH.
As we know, 
Now we have to calculate the hydroxide ion concentration.
![pOH=-log[OH^-]](https://tex.z-dn.net/?f=pOH%3D-log%5BOH%5E-%5D)
![9.9=-log[OH^-]](https://tex.z-dn.net/?f=9.9%3D-log%5BOH%5E-%5D)
![[OH^-]=antilog(-9.9)](https://tex.z-dn.net/?f=%5BOH%5E-%5D%3Dantilog%28-9.9%29)
![[OH^-]=1.258\times 10^{-10}](https://tex.z-dn.net/?f=%5BOH%5E-%5D%3D1.258%5Ctimes%2010%5E%7B-10%7D)
Therefore, the concentration of and are and respectively.
Answer: only Br2.
Justification.
In a chemical reaction the element that gains electrons experiments a reduction in its oxidation state, that is why it is said that it is reduced.
So, to know what element is being reduced you need to calculate the oxidation states of the elements involved.
Here I indicate the oxidation states of each element if the reaction putting them inside parenthesis:
Reactants side Products side
K (0) K (1+)
Br (0) Br(1-)
So, K lost one electron, increasing its oxidation statefrom 0 to 1+, meaning that it is being oxidized.
And, each atom of Br gained one electron, reducing its oxidation state from 0 to 1-, meaning it is being reduced.
Therefore, the answer is that Br2 is the substance being reduced.
