Which of the following solutions have the same concentration?

The concentration of the given solutions can be calculated in terms of molarity. Molarity is given by the formula

For option (i) Molarity of NaOH = = 2.5M

(ii) Molarity of KCl = 0.5/0.2 = 2.5M

(iii) Molarity of NaOH = = 10M

(iv) Molarity of KOH = = 1.7M

The solutions (i) and (ii) have the same concentration.