Question

Question 6
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?

(a) A, B, C
(b) B, C, D
(c) A, D, E
d) B, D, E

Answer 1

Option (b) is correct.
The element B, C, D belong to the second period because they have 2 used shells (K and L shell). 'A' belongs to period one as it has only 2 electrons hence only K shell is used. 'E' will be in period 4 (all elements in a row have equal number of shells).