In the modern periodic table, elements are arranged in order of increasing atomic number 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 periodic and 18 groups. Each period begins with the filling of a new energy shell. In accordance with the Aufbau principle filling of a new energy shell. In accordance with the Aufbau principle, the seven period (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.
Which of the elements whose atomic numbers are given below, cannot be accommodated in the present set up of the long form of the periodic table

Element                       Atomic number

     A                                         5

     B                                         7

     C                                        10

(i) Which element belongs to group 18? 

(ii) Which element belongs to group 15? 
(iii) Which element belongs to group 13? 

(iv) To which period/periods do these elements belong?