The ammonium ion $(NH_4^+)$ acts as:

The conjugate base of $H_{2}PO_{4}^{-}$ is:

Select the amphoteric substance from the following:

Which of the following substances acts as a base when reacted with water?

Acidity of $BF_3$ can be explained on the basis of which of the following concepts?

Phosphoric acid ionizes in three steps with their ionization constant values $K_{a_1}, K_{a_2}$ and $K_{a_3}$ respectively,while $K$ is the overall ionization constant. Which of the following statements are true?
$A.$ $\log K = \log K_{a_1} + \log K_{a_2} + \log K_{a_3}$
$B.$ $H_3PO_4$ is a stronger acid than $H_2PO_4^{-}$ and $HPO_4^{2-}$
$C.$ $K_{a_1} > K_{a_2} > K_{a_3}$
$D.$ $K_{a_1} = \frac{K_{a_3} + K_{a_2}}{2}$
Choose the correct answer from the options given below