Explanation:
A buffer solution is an aqueous solution consisting of a mixture of a weak acid and its conjugate base, or weak base and its conjugate acid.
Also, a buffer solution is a solution which resists changes in pH when acid or alkali is added to it.
(0.1 mol NaH₂PO₄ + 0.1 mol Na₂HPO₄) when dissolved in 1 L H₂O will produce a buffer because NaH₂PO₄ is considered as weak acid while Na₂HPO₄ is its conjugate base. 2.(0.1 mol H₃O⁺ + 0.1 mol Cl⁻) is not a mixture of a weak acid and its conjugate base, or weak base and its conjugate acid.(0.1 mol HCl + 0.1 mol NaoH) HCL is a strong acid and NaOH is a strong base so it will not form a buffer when dissolved in water. (0.1 mol H₃O⁺ + 0.1 OH⁻) is not a mixture of a weak acid and its conjugate base, or weak base and its conjugate acid(0.1 mol NaCl+ 0.1 mol KCl) NaCL and KCL are salts so it will not form a buffer when dissolved in water.So the right choice is
(0.1 mol NaH₂PO₄ + 0.1 mol Na₂HPO₄)