The conjugate acid-base pair is 

1. A pair that differs only by one proton

2. A pair that differs only by the size

3. A pair that differs only by electronegativity

4. None of the above

The conjugate bases for Brönsted acids, H₂SO₄, and HCO₃^- will be, respectively:

1. ${\mathrm{HSO}}_4^{-}$, ${\mathrm{CO}}_3^{2-}$

2.  HSO₄^-, CO₃^-

3. SO₄^-2, CO₃^2-

4. HS₂O₄^-, CO₃^2-

The conjugate acids for the Brönsted bases  ${\mathrm{NH}}_2^{-}$ , NH₃ and HCOO^– will be respectively:

1. N₂H₆, NH⁴⁺, HCOOH

2. NH₃, ${\mathrm{NH}}_4^{+}$ , HCOOH

3. NH₃, NH⁴⁺, HCOO₃

4. N₂H, NH⁴⁺, HCOOH

 OH^– , F^– , H⁺ and BCl₃ 

The species described above that contain Lewis acids are:

1. BCl₃ and F^-

2. OH^– and F^-

3. H⁺and BCl₃

4. F^- and BCl₃

The species that can act as Bronsted acids as well as bases is/are:

1.  ${\mathrm{H}}_2\mathrm{O}$

2.  ${\mathrm{HCO}}_3^{-},$ ${\mathrm{HSO}}_4^{-}$ $$

3.  ${\mathrm{NH}}_3$

4.  All of the above.