Question

the concentration of h + ions in a solution is 10 - 6 mole l-1. what is the concentration of oh- ion in it​

Answer 1

That would be a pH of 16, leaving aside the distinction between concentration and activity. That would imply a hydroxide ion activity of 100 M, which is physically implausible, so a pH of 16 seems unattainable. However, unlike what many people think, apparently including a couple of (mercifully retired) chemistry professors who answered this question, is IS possible to go above pH 14 in aqueous solution. pH 15 is not impossible, nor are negative pH’s.