Hint: We know that as per arrangement of elements in our modern periodic table, the first element of one group has similar properties as the second element of the next group has, this diagonal relationship can help us in deducing various similarities between these two diagonal elements.
Complete answer: Here, we have lithium and magnesium. As per our modern periodic table, lithium belongs to group \[I\] and magnesium belongs to group \[II.\] Both of them are positioned diagonal to each other and are known to have a diagonal relationship. We can list out some similarities between the two as follows: In their respective groups, we can see that both these elements are harder and lighter as compared to the other elements in their group. Both these elements form nitrides upon reacting with nitrogen. Electronegativity is a function of an atom's ability to draw electrons from a bonding pair. The most widely used is the Pauling scale. A value of \[4.0\] is given to fluorine (the most electronegative element), and values vary down to cesium and francium which are the least electronegative at \[0.7.\]
Note: Remember that however, all the properties are not similar such as the nature of the carbonates formed by lithium and magnesium. We also know magnesium carbonate as Magnetite and it occurs in hydrated form. We can use it as an antacid because it is basic in nature. On the other hand, lithium carbonate is not basic in nature.