Question

fill in the missing chemical formulae in the tables below.
acid\tconjugate base
base\tconjugate acid
$\ce{h_{2}po^{-}_{4}}$\t\t$\ce{so^{2-}_{4}}$\t
$\ce{h_{3}po_{4}}$\t\t$\ce{no^{-}_{3}}$\t
$\ce{h_{3}o^{+}}$\t\t$\ce{hso^{-}_{4}}$\t

Explanation:

To determine the conjugate base of an acid, the acid donates a proton ($\ce{H^+}$). To determine the conjugate acid of a base, the base accepts a proton ($\ce{H^+}$).

Step 1: Conjugate base of $\ce{H2PO4^-}$

$\ce{H2PO4^-}$ donates one $\ce{H^+}$:
$\ce{H2PO4^- -> HPO4^{2-} + H^+}$
So the conjugate base is $\ce{HPO4^{2-}}$.

Step 2: Conjugate base of $\ce{H3PO4}$

$\ce{H3PO4}$ donates one $\ce{H^+}$:
$\ce{H3PO4 -> H2PO4^- + H^+}$
So the conjugate base is $\ce{H2PO4^-}$.

Step 3: Conjugate base of $\ce{H3O^+}$

$\ce{H3O^+}$ donates one $\ce{H^+}$:
$\ce{H3O^+ -> H2O + H^+}$
So the conjugate base is $\ce{H2O}$.

Step 4: Conjugate acid of $\ce{SO4^{2-}}$

$\ce{SO4^{2-}}$ accepts one $\ce{H^+}$:
$\ce{SO4^{2-} + H^+ -> HSO4^-}$
So the conjugate acid is $\ce{HSO4^-}$.

Step 5: Conjugate acid of $\ce{NO3^-}$

$\ce{NO3^-}$ accepts one $\ce{H^+}$:
$\ce{NO3^- + H^+ -> HNO3}$
So the conjugate acid is $\ce{HNO3}$.

Step 6: Conjugate acid of $\ce{HSO4^-}$

$\ce{HSO4^-}$ accepts one $\ce{H^+}$:
$\ce{HSO4^- + H^+ -> H2SO4}$
So the conjugate acid is $\ce{H2SO4}$.

Answer:

acid	conjugate base	base	conjugate acid
$\ce{H3PO4}$	$\ce{H2PO4^-}$	$\ce{NO3^-}$	$\ce{HNO3}$
$\ce{H3O^+}$	$\ce{H2O}$	$\ce{HSO4^-}$	$\ce{H2SO4}$