ICSE Class 7 Answered

Valency is the combining capacity of an element or of a radical. Valency of an element or radical is the number of hydrogen atoms which can combine with or displace one atom of the elementor radical forming a compound.

The atomic number and the atomic mass of hydrogen is 1. There is one electron present in an atom of hydrogen. The number of valence electrons present in hydrogen atom is 1. Hydrogen atom loses this electron easily to become stable or to make bonds with other atoms. Thus on losing this one electron, positive ions are formed. Therefore, the valency of hydrogen is +1.