In the following multiple choice test, we often abbreviate $ H_3O^+ $ by $ H^+ $ (Which is actually false, indeed, $ H^+ $ is always fully hydrated in water!)
What is the hydrolysis equilibrium of citric acid ?
a) $H_3C_6H_5O_7$ $+$ $2H_2O$ 
$H_3O^+$ $+$ $H_5C_6H_5O_8^-$
b) $H_3C_6H_5O_7$ $+$ $H_2O$ $H_4C_6H_5O_7^+$ $+$ $OH^-$
c) $H_3C_6H_5O_7$ $+$ $H_2O$ $H_3O^+$ $ +$ $H_3C_6H_4O_7^-$
d) $H_3C_6H_5O_7$ $+$ $H_2O$ $H_3O^+$ $+$ $H_2C_6H_5O_7^-$
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The correct answer is: d)
$H_3C_6H_5O_7$ $+$ $H_2O$ $H_3O^+$ $+$ $H_2C_6H_5O_7^-$