Đáp án đúng: A 2,24 lít ${{\text{n}}_{{{\text{H}}_{\text{2}}}}}\,\text{=}\,\frac{\text{1}}{\text{2}}{{\text{n}}_{\text{K}}}\,\text{=}\,\frac{\text{1}}{\text{2}}\text{.}\frac{\text{7,8}}{\text{39}}\,\text{=}\,\text{0,1}\,\text{mol}\,\Rightarrow \,\text{V}\,\text{=}\,\text{2,24}\,\text{lit}$
