Hướng dẫn:

${{n}_{Mg}}=\frac{{{m}_{Mg}}}{{{M}_{Mg}}}=\frac{6}{24}=0,25\left( mol \right)$

         0,25    0,25           (mol)

Theo phương trình ta có:

${{n}_{Mg{{X}_{2}}}}={{n}_{Mg}}=0,25\left( mol \right)$

$\Rightarrow {{M}_{R{{X}_{2}}}}=\frac{{{m}_{R{{X}_{2}}}}}{{{n}_{R{{X}_{2}}}}}=\frac{23,75}{0,25}$

$2.{{M}_{R}}+{{M}_{Mg}}=95\Rightarrow {{M}_{R}}=\frac{95-{{M}_{Mg}}}{2}$

$\Rightarrow {{M}_{R}}=\frac{95-24}{2}=35,5$

R là Clo

Chọn đáp án B