Which pH value represents a solution with the lowest OHM
ion concentration?

pH value 1 represents a solution with the lowest OH⁻ion concentration.

Explanation:

pH is given by the expression as the negative logarithm to the base 10 of the concentration of hydrogen ions.

pH = -log₁₀[H⁺]

If the pH is lower than 7, pH < 7 then it is acidic

If the pH = 7, then it is neutral

If the pH > 7, then it is basic

If pH is 1 then the solution is showing mostly acidic character,which is least basic in its character.

So if the pH is 1, which is most acidic and least basic solution that is lowest OH⁻ ion concentration.

"you start with 15.67 g mgco3-xh2o, when heated and all the water is removed, you are left with 7.58 g mgco3 only.

therefore, you had 15.67 - 7.58 = 8.09g h2o  

moles of each :

7.58g mgco3 = ? moles = 7.58g / 83.4g/mole = 0.09moles  

8 09g h2o = ? moles = 8.09g / 18g/mole = 0.44moles  

molar ratio between the two by dividing both numbers by the smallest number :

0.09 / 0.09 = 1  

0.44 / 0.09 = 4.8  

mgco3-5h2o"