Đáp án đúng: C
4.
Sau các phản ứng ta thu được 5,92 gam hỗn hợp rắn nên dung dịch cuối cùng là Mg2+.
Ta có: $\displaystyle {{\text{n}}_{\text{NO}_{\text{3}}^{\text{-}}}}\text{=}\,\text{0,1}\,\text{mol}\,\,\xrightarrow{\text{BT}\,\,\,\,\text{NO}_{\text{3}}^{\text{-}}}{{\text{n}}_{\text{Mg(N}{{\text{O}}_{\text{3}}}{{\text{)}}_{\text{2}}}}}\text{=}\,\text{0,05}\,\text{mol}$
Bào toản khối lượng 3 kim loại ta có:
$\displaystyle \xrightarrow{\text{BTKL}}\text{m}\,\text{+}\,\text{0,1}\text{.108}\,\text{+}\,\text{2,4}\,\text{=}\,\,\text{10,08}\,\text{+}\,\text{5,92}\,\text{+}\,\text{0,05}\text{.24}\,\,\Rightarrow \,\text{m}\,\text{=}\,\text{4}\,\,\text{gam}$
