A) \[(A)+(B)+3{{H}_{2}}O,\]
B) \[{{C}_{2}}{{H}_{5}}CN\]
C) \[3KCl\]
D) \[C{{H}_{3}}C{{H}_{2}}CON{{H}_{2}}\]
Correct Answer: D
Solution :
Use the general term in the expansion of \[{{(x+y)}^{n}}\]is\[{{T}_{r+1}}{{=}^{n}}{{C}_{r}}{{x}^{n-r}}{{y}^{r}}\] Since, in binomial expansion of\[{{(a-b)}^{n}},n\ge 5,\]the sum of fifth and sixth terms is equal to zero. \[\therefore \]\[^{n}{{C}_{4}}{{a}^{n-4}}{{(-b)}^{4}}{{+}^{n}}{{C}_{5}}{{a}^{n-5}}{{(-b)}^{5}}=0\] \[\Rightarrow \]\[\frac{n!}{(n-4)!4!}{{a}^{n-4}}.{{b}^{4}}-\frac{n!}{(n-5)!5!}{{a}^{n-5}}{{b}^{5}}=0\] \[\Rightarrow \]\[\frac{n!}{(n-5)!4!}{{a}^{n-5}}.{{b}^{4}}\left\{ \frac{a}{n-4}-\frac{b}{5} \right\}=0\] \[\Rightarrow \]\[\frac{a}{b}=\frac{n-4}{5}\]
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