The pH of the salts in decreasing order is FeCl2, FeCl3, MgCl2, KClO2.
What is pH?
pH is an expression of hydrogen ion concentration in water. Specifically, pH is the negative logarithm of hydrogen ion (H+) concentration (mol/L) in an aqueous solution:
pH = -log10(H+)
The term is used to indicate basicity or acidity of a solution on a scale of 0 to 14, with pH 7 being neutral.
As the concentration of H+ ions in solution increases, acidity increases and pH gets lower, below 7. When pH is above 7, the solution is basic.
Because pH is a logarithmic function, one unit change in pH indicates a 10x change in H+ concentration in that solution.
However, what is actually measured is hydrogen ion activity, not concentration.
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