Identify the conjugate base of ${H_2}PO_3^-$ and the conjugate acid of ${HCO_3^-}$.

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

Acetic acid is a weak electrolyte because

Baking powder used to make cake is a mixture of starch,$NaHCO_3$,and $Ca(H_2PO_4)_2$. The function of $Ca(H_2PO_4)_2$ is

The one which has the highest value of $pH$ is

Which one of the following substances has the highest proton affinity?