:a substance that is added to a chemical reaction, that increases the rate of the reaction, that is not consumed in the reaction, and that does not affect the equilibrium in any way

Catalyst

Explanation:

A catalyst is a substance which increases the rate of a reaction by taking the reaction through a different path which has a lower activation energy .Thus more reactant molecules can cross the energy barrier and convert to products.

The catalyst itself does not take part in the chemical reaction and is regenerated as such at the end.

Catalyst does not affect the position of equilibrium.

For example:

acts as a catalyst here as it gets regenerated as such.

it have destructive character

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.