Question

The total number of electrons present in first two and last two shells is the same for an atom of an element X.The sum of the electrons present in second, fourth and fifth shells is equal to the number of electrons present in third shell and fifth shell is valence shell. To which group in the periodic table would it belong?

• A. IVA (14)
• B. IIA (2)
• C. IIIA (13)
• D. VIA (16)

Answer 1

Answer: (B)

IIA (2)

Fifth shell is valence shell: $\therefore$ Atomic configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}5s^{x}4d^{y}5p^z$

Now, $2+2+6=2+6+x+y+z\Rightarrow x+y+z=2$

Also, $2+6+2+6+y+x+z=18\Rightarrow x+y+z=2$

For element to have electrons in $4$d or $5$p, $5$s should have atleast $2$ electrons. Thus $x=2$ hence, $y+z=0$ is $y=0,z=0$

$\therefore$The element has $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}5s^2$ configuration and belongs to second group (IIA)