Which of the following is a Lewis acid but not a Bronsted acid?

$A$ tribasic acid is:

Select the set of amphiprotic species.

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 of the following is a Lewis base?

The conjugate acid of $H_2PO_4^-$ is