Following four solutions are prepared by mixing different volumes of NaOH and HCl of different concentrations. The pH of which one of them will be equal to 1?

75mLM5HCl+25mLM5NaOH

To determine which solution will have a pH of 1, we need to calculate the number of moles of HCl and NaOH in each mixture. A pH of 1 indicates a strongly acidic solution. This means we need a significant excess of HCl.

Let's analyze each option:

• 55mLM10HCl + 45mLM10NaOH:
  Moles of HCl = 55 mL * 0.1 M = 5.5 mmol
  Moles of NaOH = 45 mL * 0.1 M = 4.5 mmol
  Excess HCl = 5.5 mmol - 4.5 mmol = 1 mmol
  Total volume = 100 mL
  [H+] = 1 mmol / 100 mL = 0.01 M
  pH = -log(0.01) = 2

• 75mLM5HCl + 25mLM5NaOH:
  Moles of HCl = 75 mL * 0.05 M = 3.75 mmol
  Moles of NaOH = 25 mL * 0.05 M = 1.25 mmol
  Excess HCl = 3.75 mmol - 1.25 mmol = 2.5 mmol
  Total volume = 100 mL
  [H+] = 2.5 mmol / 100 mL = 0.025 M
  pH = -log(0.025) ≈ 1.6

• 100mLM10HCl + 100mLM10NaOH:
  Moles of HCl = 100 mL * 0.1 M = 10 mmol
  Moles of NaOH = 100 mL * 0.1 M = 10 mmol
  This is a complete neutralization; pH will be 7.

• 60mLM10HCl + 40mLM10NaOH:
  Moles of HCl = 60 mL * 0.1 M = 6 mmol
  Moles of NaOH = 40 mL * 0.1 M = 4 mmol
  Excess HCl = 6 mmol - 4 mmol = 2 mmol
  Total volume = 100 mL
  [H+] = 2 mmol / 100 mL = 0.02 M
  pH = -log(0.02) ≈ 1.7

None of the options give a pH exactly equal to 1. However, the closest option is 75 mL 0.05 M HCl + 25 mL 0.05 M NaOH, which results in a pH of approximately 1.6. There may be an error in the question or the provided options.