Which of the following species is an acid and also a conjugate base of another acid?

Which one of the following statements is not correct?

Which one of the following arrangements represents the correct order of the proton affinity of the given species?

An aqueous solution of an acid is characterized by the presence of:

When a strong acid,strong base,or their salt are dissolved in water,they are completely ionised. If a strong acid is added to a strong base,$H^{+}$ ions from the former combine with $OH^{-}$ ions of the latter forming water. The formation of each water molecule liberates a certain quantity of energy and the reaction is exothermic. The heat liberated when one mole of water is formed by combining hydrochloric acid and sodium hydroxide is $13.7 \, kcal$. The heat liberated when one mole of water is formed by combining sulphuric acid and sodium hydroxide is......$kcal$

Which one of the following is not an amphoteric substance?