3. What is the meaning of coordination number?

Explanation:

Its simple

This is the number of atoms, ions, or molecules that a central atom or ion holds as its nearest neighbours in a complex or coordination compound or in a crystal.

for example: Sodium chloride (NaCl) or table salt is an ionic compound. It means that each cation will have exactly one anion associated with it, which means the cation Na+ and the anion Cl− have the same number of coordinates.

It may be really confusing at first

I recommend you go online and watch tutorial  videos on the topic

definition

                    entropy is a measure of the randomness or the extent of disorder of a chemical process.

                      enthalpy is a measure of the heat change of a reaction occurring at a constant pressure.

measurement units:

                        entropy is measured in joule per kelvin (jk⁻¹)   whereas enthalpy is measured in joule per mole (jmol⁻¹)

requirements:

                            entropy has no requirements or limits, and its change is measured by the division between the heat change of the chemical process and the temperature.

                              in contrast, enthalpy can only be related to the heat change of the reaction under standard conditions.