question_answer

How many unpaired electrons are present in \[[Cr{{(NH)}_{3}}]B{{r}_{3}}\]

A)  1             

B)  2

C)  3             

D)  4

Correct Answer: C

Solution :

 \[[Cr{{(N{{H}_{3}})}_{5}}]B{{r}_{3}}\] Suppose oxidation state of Cr is \[x,\]then. \[x+(5\times 0)+(-1\,\times \,3)=0\] \[x-3=0\] \[x=+\,3\] \[{{\,}_{24}}Cr=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{5}},4{{s}^{1}}\] \[C{{r}^{3+}}=1{{s}^{2}}2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{3}}\] So, three unpaired electrons are present in \[[Cr(N{{H}_{3}})]B{{r}_{3}}.\]