A buffer solution was prepared. If the weak acid selected here is HNO$2,$ Ka of HNO$2=4\mathrm{.}5\backslash$times $104$

A$.$ Name the chemical required to prepare the buffer solution B$.$ What is the main characteristic of a buffer solution? C$.$ Calculate the pH value of the buffer solution when $50\mathrm{.}0$ mL$,0\mathrm{.}100$ M of HF is mixed with $30\mathrm{.}0$ mL$,0\mathrm{.}150$ M of the chemical in part $($A$)$ D$.$ Calculate the pH value of the buffer solution when $10\mathrm{.}0$ mL of $0\mathrm{.}100$ M of HCl was added to the solution