pH value of 0.1 N HCl solution is approximately:

Explanation

## Page 43 The pH of an aqueous solution is calculated by the following formula: $$ pH = -\log_{10} [H^+] $$ In 0.1 N HCl solution— $$ [H^+] = 0.1 mol L^{-1} $$ Calculation of pH: $$ pH = -\log_{10} (0.1) = -\log_{10} (10^{-1}) = -(-1) = 1 $$ Thus, the pH of 0.1 N HCl is 1.0, which matches option (b). Change in pH, $\Delta(pH) = pH_2 - pH_1 = 6 - 3 = 3$; Ratio of H⁺ ion concentration, $$ \frac{pH_2}{pH_1} = \frac{\log[H^+]_2}{\log[H^+]_1} = 10^{-3} = 0.001 = \frac{1}{1000} $$ Therefore, the concentration of H⁺ ions will decrease 1000 times.