Substances which have the ability to reduce other substances are called reducing agents. These are also called as electron donors because they donate electrons to other substances.
Example: NaBH₄, LiAlH₄ and metals like Palladium, Platinum.

A chemical bond may be defined as the force of attraction between the two atoms that binds them together as a unit called molecule

Atoms of nobel gases have little or no tendency to combine with each other or with atoms of other elements. This means that these atoms must be having stable electronic configuration. So they are inert in nature.

Chemical bonds are divided into two. One is strong bond and another one is weak bond. The strong bond is further divided into ionic bond, covalent bond, coordinate bond and metallic bond. Weak bond is divided into Hydrogen bond and Van der walls interaction.

1. The tendency of atoms to have eight electrons in the valence shell is known as the 'Octet rule' or the 'Rule of eight'.
2. For example, Sodium with atomic number 11 will readily loose one electron to attain Neon's stable electronic configuration.

The compounds containing coordinate covalent bonds are called coordinate compounds.
(a) Physical state - These compounds exist as gases, liquids or solids.
(b) Electrical conductivity - Like covalent compounds, co-ordinate compounds also do not contain charged particles (ions), so they are bad conductors of electricity.
(c) Melting point - These compounds have melting and boiling points higher than those of purely covalent compounds but lower than those of purely ionic compounds.
(d) Solubility - Insoluble in polar solvents like water but are soluble in non-polar solvents like benzene, CCI_4, and toluene.
(e) Reactions - Coordinate covalent compounds undergo molecular reactions which are slow.

Greater the charge of the cation greater will be the covalent character

Ionic compounds have high melting and boiling point. (or)
Covalent compounds have low melting and boiling point

In the formation of compounds, the valence electrons of an atom involve in bonding

CrO₃. It is an oxidising agent where as other three are reducing agents

Water. It is polar solvent where as others are non-polar solvents