Periodic Classification and Elements

In coordination complexes, the central metal atom/ion exhibits primary valency (oxidation state) satisfied by anions and secondary valency (coordination number) satisfied by ligands (donor molecules). Since all these properties are characteristic of metal complexes, 'all of these' is correct.

The chemical symbol for Sodium is Na, derived from the Latin word Natrium.

The atomic number of an element is defined by the number of protons in the nucleus of its atoms. This number uniquely identifies the element.

Fluorine is a highly reactive halogen, which is a type of non-metal located in Group 17 of the periodic table.

Yttrium is a chemical element with the atomic number 39, and its chemical symbol is Y.

Mercury is a metal that is liquid at room temperature, meaning it has a very low melting point (-38.83 degrees Celsius) compared to the other elements listed.

Hydrogen is the lightest element and makes up most of the universe (about 90% of the universe is made of hydrogen).

Boron is a non metal belonging to the p block. Being a non metal it is a poor conductor of electricity at room temperature but a good conductor at high temperature. The element is not found free in nature, but occurs as orthoboric acid which is usually found in certain volcanic spring water and as borates in boron and colemantie.

The elements of  Group 7  are known as halogens. The term halogen means salt-former and compounds containing halogens are called salts. The halogens exist, at room temperature, in all three states of matter - Gases such as Fluorine & Chlorine, Solids such as Iodine and Astatine and Liquid as in Bromine. The Halogen elements on the Periodic Table are: Fluorine, Chlorine, Bromine, Iodine, Astatine.

The existence of elements in two or more different forms is called allotropy & nthe different forms are called allotropes. In the case of oxygen, there are two forms: 'normal' dioxygen (O₂) and ozone, or trioxygen (O₃). These two allotropes have different molecular configurations. More commonly, allotropy occurs because of different crystal structures in the solid, and is particularly prevalent in groups 14, 15, and 16 of the periodic table. In some cases, the allotropes are stable over a temperature range, with a definite transition point at which one changes into the other. For instance, tin has two allotropes: white (metallic) tin stable above 13.2°C and grey (nonmetallic) tin stable below 13.2°C. This form of allotropy is called enantiotropy.Carbon also has two allotropes - diamond and graphite - although graphite is the stable form at all temperatures. This form of allotropy, in which there is no transition temperature at which the two are in equilibrium, is called monotropy.

Oxygen, sulphur, selenium, tellurium and polonium constitute the group 16 of the periodic table of elements. The first four elements are collectively called CHALCOGENS. The name derives from the Greek word for bronze and points to the association of sulphur and its congeners with copper. All these are non-metallic in character. The metallic character increases down the group. The last element of the family, polonium has metallic character and is a radioactive element with a very short life period.

An element is a pure substance consisting entirely of atoms that have the same number of protons in their atomic nuclei. Molecules and compounds can consist of different types of atoms.

The atomic number of an element is equal to the number of protons in its nucleus. In a neutral atom, the number of protons equals the number of electrons, so nitrogen with 7 electrons has an atomic number of 7.

Sodium chloride (NaCl) is a compound formed by the chemical bonding of sodium and chlorine. Carbon, oxygen, and potassium are all individual elements.