Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): The solution obtained by mixing 100 mL of 0.1 M H ₃ PO ₄ and 150 mL of 0.1 M NaOH is not a buffer. Reason (R): The resulting solution contains an equimolar mixture of NaH ₂ PO ₄ and Na ₂ HPO ₄ . In the light of the above statements, choose the most appropriate answer from the options given below:

Step-by-step solution

Let us calculate the millimoles (mmol) of the acid and base mixed: mmol of H ₃ PO ₄ = 100 mL 0.1 M = 10 mmol mmol of NaOH = 150 mL 0.1 M = 15 mmol First equivalent of neutralization H ₃ PO ₄ + NaOH NaH ₂ PO ₄ + H ₂ O 10 mmol of H ₃ PO ₄ reacts with 10 mmol of NaOH to form 10 mmol of NaH ₂ PO ₄ . Remaining NaOH = 15 - 10 = 5 mmol . Second equivalent of neutralization NaH ₂ PO ₄ + NaOH Na ₂ HPO ₄ + H ₂ O The remaining 5 mmol of NaOH reacts with 5 mmol of the newly formed NaH ₂ PO ₄ to produce 5 mmol of Na ₂ HPO ₄ . R