Answer : The hydroxide ion concentration of a solution is, 
Explanation :
As we know that:
pH : It is defined as the negative logarithm of hydrogen ion concentration.
Mathematically,
![pH=-\log [H^+]](https://tex.z-dn.net/?f=pH%3D-%5Clog%20%5BH%5E%2B%5D)
Similarly,
pOH : It is defined as the negative logarithm of hydroxide ion concentration.
Mathematically,
![pOH=-\log [OH^-]](https://tex.z-dn.net/?f=pOH%3D-%5Clog%20%5BOH%5E-%5D)
Given:
pOH = 6.42
![6.42=-\log [OH^-]](https://tex.z-dn.net/?f=6.42%3D-%5Clog%20%5BOH%5E-%5D)
![[OH^-]=3.8\times 10^{-7}M](https://tex.z-dn.net/?f=%5BOH%5E-%5D%3D3.8%5Ctimes%2010%5E%7B-7%7DM)
Therefore, the hydroxide ion concentration of a solution is, 
<u>Given information:</u>
Mass of H2 = 2 g
Mass of O2 = 32 g
<u>To determine:</u>
Mass of H2O2 produced
<u>Explanation:</u>
The reaction between H2 and O2 can be given as:
H2 + O2 → H2O2
Based on the reaction stoichiometry:
1 mole of H2 reacts with 1 mole of O2 to form 1 mole of H2O2
# moles of H2 = mass of H2 / molar mass of H2 = 2 g/ 2 g.mol-1 = 1 mole
# moles of O2 = mass of O2/ molar mass of O2 = 32 g/ 32 g.mol-1 = 1 mole
Hence for the given reactant conditions, moles of H2O2 produced = 1
Mass of H2O2 = moles of H2O2 * molar mass H2O2 = 1 mole * 34 g.mole-1 = 34 g
<u>Ans</u>: 34 g of H2O2 is produced in this reaction