The minimum amount of energy required to start a chemical reaction is called

Activation energy

Explanation:

Activation energy is the extra energy that must be supplied to reactants in order to cross the energy barrier and thus convert to products.

The reactants must acquire the extra energy so as to cross the energy barrier and then only chemical reaction occurs and products are formed.

Addition of catalyst increases the rate of a reaction by taking the reaction through a different path which involves lower activation energy and thus more molecules can cross the energy barrier and convert to products.

periodic trends is an atom that gets larger as the number of electronic shells increase, the radius of atoms increases as you go down a certain group in the periodic table of elements. in general, the size of an atom will decrease as you move from left to right of a certain period.