Why do elements in the same group of the periodic table have similar properties?

Explanation:

Elements present in same group have same number of valence electrons and it is the valence electrons that determine the reactivity of an element.

For example, elements fluorine, chlorine and bromine are all group 17 elements.

Each of them contains 7 valence electrons and hence, all of them needs to gain one electron each in order to complete their octet, respectively.

Hence, we can conclude that elements in the same group of the periodic table have similar properties because they have same number of valence electrons.

out of these options:

ability to burn paper

pure sodium reacting violently with water

the boiling point of water

helium does not tend to react with anything

i would say this is a physical property:

helium does not tend to react with anything

why? :

i said helium does not tend to react with anything because well, it reacts to ! but ability to burn paper, pure sodium reacting violently with water, & the boiling point of water are chemical or

physical properties: the properties of a substance that can be observed without changing the chemical makeup of the substance

chemical properties: properties of a substance relating to the chemical nature and reactivity of the substance