Question: 53. Which among the following electronic configurations belong to main group elements?
A. [\mathrm{Ne}] 3 \mathrm{s}^{1}
B. [\mathrm{Ar}] 3 \mathrm{d}^{3} 4 \mathrm{s}^{2}
C. [\mathrm{Kr}] 4 \mathrm{d}^{10} 5 \mathrm{s}^{2} 5 \mathrm{p}^{5}
D. [\mathrm{Ar}] 3 \mathrm{d}^{10} 4 \mathrm{s}^{1}
E. [\mathrm{Rn}] 5 \mathrm{f}^{0} 6 \mathrm{d}^{2} 7 \mathrm{s}^{2}
Choose the correct answer from the options given below:
(1) B and E only
(2) A and C only
(3) D and E only
(4) A, C and D only
Answer: Option (2)
Explanation:
Main group elements are those in which the last electron enters only the s or p subshell.
These include elements of groups 1,
2 and 13 to 18.
Statement A: [\mathrm{Ne}] 3s^{1} represents sodium,
where the last electron enters the s-subshell.
Sodium belongs to group 1, a main group element.
Hence, A is correct.
Statement B: [\mathrm{Ar}] 3d^{3} 4s^{2} shows that electrons are entering the d-subshell.
This corresponds to a transition metal, not a main group element.
Hence, B is incorrect.
Statement C: [\mathrm{Kr}] 4d^{10} 5s^{2} 5p^{5} indicates that the last electron enters the p-subshell.
This configuration belongs to a halogen in group 17,
which is a main group element. Hence, C is correct.
Statement D: [\mathrm{Ar}] 3d^{10} 4s^{1} corresponds to copper,
where a filled d-subshell is present.
Copper is a transition metal and not considered a main group element.
Hence, D is incorrect.
Statement E: [\mathrm{Rn}] 5f^{0} 6d^{2} 7s^{2} shows electron entry into the d-subshell, characteristic of transition elements, not main group elements.
Hence, E is incorrect.
Therefore, the correct configurations belonging to main group elements are A and C only.
So, the correct option is (2).