Modern periodic rule states that, 'The physical and chemical properties of the elements are the periodic function of their atomic number'.

A chemical reaction in which a single reactant is broken down into two or more products called a decomposition reaction. For example:

CaCO₃ -------> CaO + CO₂
CuCO₃ -------> CuO + CO₂

A catalyst is a chemical substance that increases or decreases the rate of a chemical reaction without taking part in a chemical reaction.

The +ve catalyst is the chemical substance that increases the rate of a chemical reaction. For example MnO₂. The catalyst is the chemical substance that decreases the rate of a chemical reaction. For example glycerine.

The electrons present in the outermost shell or valence shell of an atom are called valence electrons.

In a period, valency increases up to the 4th group and decreases up to the 8th group and again increases.

We know, water breaks down into hydrogen and oxygen during its electrolysis. As two elements decompose themselves in this chemical reaction, it is called a decomposition reaction.

2H₂0 --------> 2H₂ + O₂

Increasing order of atomic weight was the basis of Mendeleev's periodic table.

A chemical reaction in which aid and base react together to gee salt and water is called an acid-base reaction.

It is called a neutralization reaction because the acidic and basic nature of compounds is neutralized during the reaction.