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 Arfbau 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.


The elements with atomic numbers 35, 53 and 85 are all ________.


From the periodic table and their electronic configuration is can be easily determined that they are halogens.

[Ar]4s2 4p5=35


[Kr]5s25p5=53


[Xe]6s26p5=85


As the p orbitals has 5 electrons and there are 7 electrons in the last shells therefore these are group 17 elements which are also called halogens.

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