question_answer

In an element 'X', \[{{\text{5}}^{\text{th}}}\] electron of\[{{\text{3}}^{\text{rd}}}\], shell is its last electron. In another element 'Y',\[{{7}^{th}}\] electron of\[{{\text{3}}^{\text{rd}}}\]shell is its last electron. Then (a) Identify 'X' and 'Y'. (b) Write the formula of the compound formed by the combination of 'X' and 'Y'.    (c) What is the atomicity of 'X' and' 'Y'? (d) Find the ratio of number of neutrons of 'Y' to 'X'.  \[\frac{A}{2Z}=1\Rightarrow A=2Z\]

	\[a\]		\[b\]	\[c\]		\[d\]
	\[X\]	\[Y\]		\[X\]	\[Y\]
(a)	Phosphorus	Chlorine	\[X{{Y}_{3}}\]	4	2	9:8
(b)	Phosphorus	Chlorine	\[X{{Y}_{2}}\]	3	2	7:8
(c)	Boron	Fluorine	\[X{{Y}_{3}}\]	4	2	9:8
(d)	None

Answer:

In X?,\[{{5}^{th}}\]electron of 3rd shell is its last electron \[\Rightarrow \] \[E.C.=2,\text{ }8,\text{ }5\] In ?Y?,\[{{7}^{th}}\]electron of 3rd shell is its last electron\[\Rightarrow \] \[E.C.=2,\text{ }8,\text{ }7\] (a) The no. of electrons in X and Y are 15 and 17 respectively. Hence, X and Y are phosphorus and chlorine respectively. (b) \[X{{Y}_{3}}\] (c) 4 (\[{{P}_{4}}\]) and 2 (\[C{{l}_{2}}\]) respectively. (d) No. of neutrons in X i.e., \[P=31-15=16;\] No. of neutrons in Y i.e., \[Cl=35-17=18\] Therefore, the ratio\[=Y:X=9:8\].