Periodic Classification and Elements

In 1817, Johann Wolfgang Dobereiner, a German chemist, tried to arrange elements with similar properties into groups called triads having 3 elements each.

Copper is placed along with potassium in group I of Mendeleev’s periodic table.

Mendeleev classified elements on the basis of their atomic mass and chemical properties. 

The properties of an element depend on the valence electrons or the number of electrons in the outermost orbit. In a group of modern periodic table, all the elements have the same number of valence electrons. For example, all alkali elements have one electron in their outermost orbit. Hence, they have similar properties.

The mentioned element should have 3 shells and 6 valence electrons in the outermost shell. It must gain two electrons to attain a stable electronic configuration of 8 electrons in the outermost shell. Such elements which tend to gain one or more electrons are non-metals, so the mentioned element must be a non-metal.

Group 17 elements are known as halogens.

IUPAC (International Union of Pure and Applied Chemistry) approves the names of the elements. 

Out of these elements, only nitrogen does not possess any allotropic modification.

Sixth period is the longest period in the modern periodic table.

19 is the atomic number of potassium, which is an alkali metal. So, option 3 is the possible answer.

Eight elements are present in the 3^rd period of the modern periodic table.

Atomic numbers 11 and 19 belong to the elements of first group of the periodic table.

The element with electronic configuration 2, 8, 8, 1 will be most electropositive as after the loss of an electron, it will acquire stable configuration.

The number of electrons in the valence shell of an element indicates the group to which an element belongs.

Electron affinity decreases down a group because due to increase in atomic size, the force of attraction between the nucleus and the electrons to be added becomes less.