Why do elements in the same group have similar physical and chemical properties?

Which of the following pairs of elements belongs to the group of representative elements in the periodic table?

What is the correct order of basicity of halides?

Consider the following four elements,which are represented according to the long form of the periodic table. Here $W$,$Y$,and $Z$ are left,up,and right elements with respect to the element $X$,and $X$ belongs to the $16^{th}$ group and $3^{rd}$ period. Then,according to the given information,the incorrect statement regarding the given elements is:

The order of reactivity of $K$,$Mg$,$Zn$,and $Au$ with water is

The correct order of acidic strength is: