Question

The elements with atomic number 39 to 48 belong to:
A.Fourth period
B.Fifth period
C.Sixth period
D.Third period

Answer 1

Maximum value of n from an electronic configuration of an element represents its period. For example: Electronic configuration of atomic number 39 is $4{{\text{d}}^1}5{{\text{s}}^2}$ .

Complete step by step answer:
In modern periodic tables, elements are arranged in such a way that the physical and chemical properties of an element are periodic functions of its atomic number. Modern periodic table consists of 18 vertical columns or groups and 7 periods. Elements belong to the same group having the same number of electrons in the outermost shell so their properties are similar. Period 1 has 2 elements and extends from atomic number 1 to 2. Period 2 has 8 elements and extends from atomic number 3 to 10. Period 3 has also 8 elements and extends from atomic number 11 to 18. Period 4 has 18 elements and extends from atomic number 19 to 36. Period 5 also has 18 elements and extends from atomic number 37 to 54. Period 6 has 32 elements and extends from atomic number 55 to 86. Period 7 at present has 26 elements and extends from atomic number 87 to 112.

PERIOD	Period Subshell	Number of elements
1	1s	2
2	2s,2p	8
3	3s, 3p	8
4	4s, 3d, 4p	18
5	5s, 4d, 5p	18
6	6s, 4f, 5d, 6p	32
7	7s, 5f, 6d	26

Elements of group 1 to 2 are known to be s block elements where elements of group 1 are known as alkali metal and elements of group 2 are known as alkaline earth metal. Elements belong from group 13 to 18 are known to be p block elements. Elements of group 18 are also known as inert gases. D block starts from group 3 to group 12 and extends from period 4 to period 7. F block elements all have group 3 and extend from period 6 to 7.

Thus, the correct option is B.

Note:
Atomic number from 39 to 48 is from Yttrium to Cadmium. These have period number 5 and belong to a 4f series of d block elements.