Question

The valency of an element is:
(E) The mass of element displacing 1 part by the mass of hydrogen
(F) The mass of the element combining with 8 parts by mass of oxygen
(G) The number of atoms of hydrogen combining with 1 atom of the given element
(H) The number of atoms in 1 molecule of the given atom

Answer 1

Valence is electrons present in the outermost shell. An atom uses its valence electrons to combine with other atoms. Oxygen has valency as 2 because it can combine with hydrogen atoms to form water.

Complete solution step by step:
Valency indicates the number of electrons present in valence or outermost shells.
Valence electrons participate in chemical bonding and they are used in combining with atoms of other elements.
Elements having completely filled outermost shells have valency as zero as they do not combine with any atoms like helium, Neon.
Number of electrons shared, gained or lost to complete the outermost shell is valency.
Carbon has an atomic number as 6 and has four electrons in the outermost shell; it combines with four hydrogen atoms to form methane and completes its outermost shell.
Oxygen has an atomic number as 8 and has six electrons in the outermost shell, it combines with two hydrogen atoms to form water and completes its outermost shell.
Fluorine has atomic number as 9 and has seven electrons in the outermost shell, it combines with one hydrogen atom to form Hydrogen Fluoride.

So, The valency of an element is (C ) The number of atoms of hydrogen combining with 1 atom of the given element.

Note: Every atom of an element has different combining capacity which is called valency. Lithium, sodium, potassium has valency as 1. Magnesium, barium have valency as 2. Halogens have valency as 1 and inert gases have valency as 0. Carbon has valency as 4. In periodic table, valency increases from 1 to 4 then decreases from 4 to zero.