Assuming equal concentrations, arrange these solutions by pH.

NH3 (aq)

Sr(OH)2 (aq)

HBr (aq)

HCN (aq)

KOH (aq)

The pH of solution often differs. Assuming equal concentrations, The rank these solutions by pH are in the order of Highest pH to Lowest pH are  Sr(OH)2(aq), KOH (aq), NH3(aq), HCN (aq) and HBr (aq).

The Strong electrolytes often dissociate fast in water when compared to the weak electrolytes that often dissociate partially.

Acids are known to have pH value smaller than 7, bases are known to have pH value greater than 7, and neutral salts have a pH value  of 7.

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Highest pH(most basic)

Sr(OH)2(aq)

KOH (aq)  

NH3(aq)

HF (aq)  

HClO4(aq)

Lowest pH(most acidic)

Explanation:

The concentration of H+ ion will determine the pH of a solution. The pH actually reflects the ratio of H+ ion and OH- since both of them can combine into water. Solution with more H+ ion will have a lower pH and called acidic, while more OH- will have high pH and be called basic. Strong acid/base will be ionized more than weak acid/base.

Sr(OH)2(aq) = strong base, release 2 OH- ion per mole

KOH (aq) = Strong base, release 1 OH- per mole

NH3(aq) = weak base, release less than 1 OH- per mole

HF (aq) =strong acid, release 1 H+ per mole

HClO4(aq) = stronger acid, release 1 H+ per mole