Comprehension given below is followed by some multiple choice questions. Each question has one correct option. Choose the correct option. In the modern periodic table, elements are arranged in order of increasing atomic numbers which is related to the electronic configuration. Depending upon the type of orbitals receiving the last electron, the elements in the periodic table have been divided into four blocks, viz $s, p, d$ and $f$.

The modern periodic table consists of 7 periods and 18 groups. Each period begins with the filling of a new energy shell. In accordance with the Aufbau principle, the seven periods ( 1 to 7 ) have $2,8,8,18$, 18,32 and 32 elements respectively.

The seventh period is still incomplete. To avoid the periodic table being too long, the two series of $f$-block elements, called lanthanoids and actinoids are placed at the bottom of the main body of the periodic table

(v) The elements with atomic numbers 35,53 and 85 are all ............ .

Electronic configuration of four elements $A, B, C$, and $D$ are given below

A. $1 s^2 2 s^2 2 p^6$

B. $1 s^2 2 s^2 2 p^4$

C. $1 s^2 2 s^2 2 p^6 3 s^1$

D. $1 s^2 2 s^2 2 p^5$

Which of the following is the correct order of increasing tendency to gain electron?

Which of the following elements can show covalencey greater than 4 ?

Those elements impart colour to the flame on heating in it, the atoms of which require low energy for the ionisation (i.e., absorb energy in the visible region of spectrum). The elements of which of the following groups will impart colour to the flame ?

Which of the following sequences contain atomic numbers of only representative elements?