Question

Elements in period have same:
A. number of valence electrons
B. valency
C. number of shells
D. volume

Answer 1

The elements existing in nature are arranged in a specific way in periodic table depending upon their physical and chemical properties. The horizontal rows are called periods and the vertical columns are called groups.

Complete answer:
Elements having similar outer electronic configuration in their atoms are arranged in vertical columns, referred to as groups or families.
The period in the table indicates the value of n for the outermost or valence shell. In other words, a successive period in the periodic table is associated with the filling of the next higher principal energy level (n=1,n=2 etc.). It can be readily seen that the number of elements in each period is twice the number of atomic orbitals available in the energy level that is being filled. The first period (n=1) starts with the filling of the lowest level (1s) and therefore has two elements:-hydrogen ( $1{s^1}$ ) and helium has ($1{s^2}$ ) when the first shell (K) is completed.
The second period (n=2) starts with lithium and the third electron enters 2s orbital, similarly beryllium, born and neon are filled with electrons when the L shell is completed at neon giving it an at most stable configuration of inert gas. Successive filling occurs till n=7 which is the total number of periods in the periodic table.
Hence we can conclude that every element in a period has the same number of shells.

_Therefore the correct option is C. _

Note: The principal quantum number(n) defines the main energy level known as shell. The electron in an atom is characterized by four quantum numbers.