Describe where to look on the periodic table to find elements which have similar reactivity and other properties. give an example of three elements that have those similarities.

In the Periodic Table, elements with similar reactivity and similar properties are found under the same column.
In fact, elements in the same columns are said to be in the same "group", and they have the same number of valence electrons, i.e. the same number of electrons in the outermost shell. This is the main characteristics that determine how an element reacts with other elements.
For instance, Litium (Li), sodium (Na) and potassium (K) are all in the first group, and they both have 1 valence electrons. This means they can easily give away this electron to an atom of another element forming bonds with it, and therefore they have high reactivity. Instead, elements of the 8th group are called "noble gases", and they all have similar properties: they all have the outermost shell full of eletrons, so they have zero valence electrons and so they have little or no reactivity at all. Example of elements in this group are Neon (Ne) and Argon (Ar).