Answer:
1,2,3,4,5 and 6.
Explanation:
If a solution having pH values such as 1,2,3,4,5 and 6 indicates that the solution has the highest concentration of hydrogen ions because below pH 7 the concentration of hydrogen ions increases and the solution tends to more acidic. Highest concentration of hydrogen ions are present in a solution having pH 1 and when the pH value increases from pH 1, the concentration of hydrogen ions decreases.
