Which of the following mixture is not a buffer solution
A. `100 mL` of `0.5 N CH_(3)COOH + 100 mL ` of `0.05 N NaOH`
B. `100 mL` of `0.6 N HCN + 100 mL` of `0.4 NaOH`
C. `100 mL` of `0.5N NH_(4)OH + 10 mL` of `0.2 NCH_(3)COOH`
D. `100 mL` of `0.4 N HCL + 100 mL` of `0.4N NaOH`
