This Is a Certified Answer

Certified answers contain reliable, trustworthy information vouched for by a hand-picked team of experts. Brainly has millions of high quality answers, all of them carefully moderated by our most trusted community members, but certified answers are the finest of the finest.
Group of an element can be calculated based on the number of valency electrons present in the atom of the element.

the electron configuration is written - by filling the orbitals and shells - with the electrons the atom has.  Then the number of valency electrons in the outer most shell of the atom, is the group of the atom.

Hydrogen has  1 electron in shell K = 1,  1s1.  Hence it is in group 1.
Chlorine has  7 valency electrons in it. It is in group 7.  It has 17 electrons. as: 1s2,  2s2, 2p6, 3s2, 3p5. 

1 5 1