Question

Which of the given elements a, b, c, d and e with atomic number 2, 3, 7, 10 and 30 respectively belong to the same period?

Answer 1

At no. of elements a,b,c,d,e are 2,3,7,10,30.
Elements b , c , d belongs to the same period because the no. of valence shells are all 2.

Answer 2

The element b, c and d are belongs to the same period.

• The electronic configuration of element a having atomic number 2 is $1s^2$. So, it has its valance electron in 1s shell.
• The electronic configuration of element b having atomic number 3 is $1s^22s^1$. So, it has its valance electron in a 2s shell.
• The electronic configuration of element c having atomic number 7 is $1s^22s^22p^3$. So, it has its valance electron in a 2p shell.
• The electronic configuration of element d having atomic number 10 is $1s^22s^22p^6$. So, it has its valance electron in a 2p shell.
• The electronic configuration of element e having atomic number 30 is $1s^22s^22p^63s^23p^64s^23d^{10}$. So, it has its valance electron in a 4s shell.
• So, elements b, c and d have the valance electron in 2 subshells so, they belong to the same period.