Đáp án đúng: B
33,33%.
Số mol O2 và Cl2: x và y
BTKL: 32x + 71y = 2,61 gam (1)
$\displaystyle \begin{array}{l}\text{Mg }\xrightarrow{{}}\text{ M}{{\text{g}}^{\text{+2}}}\text{+ 2e}\\\text{0,02}\,\,\,\,\,\,\,\,\,\,\xrightarrow{{}}\,\,\,\,\,\,\,\,\,\,\text{0,04}\end{array}$
$\displaystyle \begin{array}{l}\text{Fe }\to \text{ F}{{\text{e}}^{\text{+2}}}\text{+ 2e}\\\text{t}\,\,\,\,\,\,\,\,\xrightarrow{{}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{2t}\end{array}$
$\displaystyle \begin{array}{l}\text{F}{{\text{e}}^{\text{2+}}}\text{+ A}{{\text{g}}^{\text{+}}}\xrightarrow{{}}\text{ F}{{\text{e}}^{\text{3+}}}\text{+ Ag}\\\,\text{t}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\xrightarrow{{}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{t}\end{array}$
$\displaystyle \begin{array}{l}\,\,\,\text{Fe }\,\,\,\,\to \text{ }\,\text{F}{{\text{e}}^{\text{+3}}}\text{+ 3e}\\\text{0,03-t}\,\,\,\xrightarrow{{}}\,\,\,\,\,\,\,\,\,\,\,\,\text{0,09-3t}\end{array}$
$\displaystyle \begin{array}{l}\text{A}{{\text{g}}^{\text{+}}}\text{+ }\,\,\text{C}{{\text{l}}^{\text{-}}}\xrightarrow{{}}\text{AgCl}\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{2y }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\to ~~\text{2y}\end{array}$
BT electron:$\displaystyle \text{4x + 2y = 0,04+2t+3}\left( \text{0,03-t} \right)\text{ }\!\!~\!\!\text{ }\left( \text{2} \right)$
KL kết tủa$\displaystyle \text{108t+ 143,5}\text{.2y}\,\text{=}\,\text{9,69}$
$\Rightarrow \text{x=0,015;}\,\text{y=0,03}\Rightarrow {\scriptstyle{}^{\text{o}}\!\!\diagup\!\!{}_{\text{o}}\;}{{\text{V}}_{{{\text{O}}_{\text{2}}}}}\text{=33,33}{\scriptstyle{}^{\text{o}}\!\!\diagup\!\!{}_{\text{o}}\;}$
