(a) A diagonal relationship in chemistry is like finding similarities between two elements that sit diagonally across each other on the periodic table.
(b) It happens because these elements have something in common. They both have similar numbers of electrons arranged in a way that makes them behave similarly.
(c) Two examples:
1. Lithium (Li) and Magnesium (Mg): Even though they are in different groups, they act alike because they both easily lose electrons.
2. Boron (B) and Silicon (Si): Despite being in different groups, they share some similarities in the way they form compounds because of their electron arrangements.
In simple terms, diagonal relationships are about finding surprising chemistry buddies in unexpected places on the periodic table.