When `Na_2CO_3 ` aqueous solution is being titrated with hydrochloric acid
`{:("Column-I " , "Column-II") ,((A) " At the start of titration", (P) " Buffer solution of " HCO_3^(-) and CO_3^(-2)),((B) "Before the first equivalent point " , (Q) "Buffer solution "H_2CO_3and HCO_3^(-) ), ((C) "At the first equivalent point",( R ) "Amphiprotic anion "pH =(1//2) (p^(ka_1) +p^(Ka_2))), ((D) "Between first and second equivalent points" , (S) "Hydrolysis of "CO_3^(-2)) :}`

Answer

A-S; B-P; C-R; D-Q

Explanation

At the start only ` CO_3^(2-) ` is present and gets hydrolysed
` CO_3^(2-) + H^(+) to HCO_3^(-) `
until ` 1^(st) ` equation pt, both are present i.e., buffer of ` HCO_3^(-) and CO_3^(2-) `
At Ist equation pt only `HCO_3^(-) ` present amphiprotic anion
after Ist eq pt, untill 2nd equation pt
` HCO_3^(-) +HCl to H_2CO_3`
i.e., buffer of `H_2CO_3 and HCO_3^(-) `