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Q.
Which of the following cannot act both as Bronsted acid and as Bronsted base?
Equilibrium
Solution:
$HCl$ can only act as Bronsted acid because it can only donate proton.
$\underset{\text{Acid}}{HCl} +\underset{\text{Base}}{ H _{2} O} \rightleftharpoons H _{3} O ^{+}+ Cl ^{-}$
The remaining options contains substances which act both as Bronsted acid and Bronsted base.
(a) $HCO _{3}^{-}+ HCO _{3}^{-} \rightleftharpoons H _{2} CO _{3}+ CO _{3}^{2-}$
(b) $NH _{3}+ NH _{3} \rightleftharpoons NH _{4}^{+}+ NH _{2}^{-}$
(c) $HSO _{4}^{-}+ HSO _{4}^{-} \rightleftharpoons H _{2} SO _{4}+ SO _{4}^{2-}$