The number of species of the following that can act both as Bronsted acids and bases is ( HCl , ClO ₄⁻,- OH , H ⁺, H ₂ O , HSO ₄⁻, SO ₄²⁻ ), ( H ₂ SO ₄, Cl ⁻ )

Step-by-step solution

(i) ( HCl H ⁺+ Cl ⁻ ) (Bronsted acid) (ii) ( ClO ₄⁻+ H ⁺ HClO ₄ ) (Bronsted base) (iii) ( O H + H ⁺ H ₂ O ) (Bronsted base) (iv) ( H ₃ O ⁺ H ⁺+ H ₂ O ) (Bronsted acid) (vii) ( H ⁺+ SO ₄²⁻ HSO ₄⁻ ) (Bronsted base) (viii) ( H ₂ SO ₄ H ⁺+ HSO ₄⁻ ) (Bronsted acid) (ix) ( Cl ⁻+ H ⁺ HCl ) (Bronsted base) Hence, ( H ₂ O ) and ( HSO ₄⁻ )(two species act as acid as well as base).