A solution containing which of the following pairs of species could be a buffer H+ Cl- , H2CO3 & HCO3- , Na+ & NO3-,Na+ & OH-,HNO3 & NO3-?

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Explanation: 

A buffered solution is made up of a weak acid and its conjugate base ( or weak base and its conjugate acid ) .Carbonic acid (H2CO3) and bicarbonate ion (HCO3- ) are the examples of this type of pairing .

H+ and Cl- represents strong acids and the conjugate base pair so this cannot make a bufffer solution .

HNO3 and NO3- are also strong acid and its conjugate base pair

Na and NO3- is a salt

Na+ and OH- is a strong base

So, H2CO3 and HCO3- carbonic acid and bicarbonate ion is the only example of a buffer solution since it is made up of a weak acid H2CO3 and its conjugate base HCO3- .

 

Answer: 

H2CO3 & HCO3- since H2CO3 is a weak  acid and HCO3- is its conjugate base.