Which elements have the most similar chemical properties

Elements that belong to the same GROUP of the periodic table have the most similar chemical properties.

Explanation:

A GROUP in the periodic table is a column of elements with the same number of valence electrons. Since electrons are exchanged/shared during a chemical reaction, then elements with similar valence electrons, will react similarly. Thus elements belonging to the same GROUP are most similar in the way they react.

For example: Sodium and Lithium are group 1 elements while fluorine and chlorine are group 17 elements. In a reaction under normal conditions, Sodium and Lithium will both try to give up their single valence electron to form cations. In doing so they will react more similarly. On the other hand, Fluorine and Chlorine who are more inclined to accept a single electron to form cations react less like the group 1 elements and more like each other.

- decrease the number of plants and animals living in the water.

< > according to newton's third law of motion, forces always act in equal but opposite pairs. another way of saying this is for every action, there is an equal but opposite reaction.< >