Explanations:
Elements in a periodic table are arranged vertically in groups and horizontally across periods.
The reactivity of the metals decreases from group 1 to group 18. According to the given elements, Lithium(Li), Sodium(Na) and Potassium (K) all belong to group 1 of the periodic table showing that they are more reactive than Magnesium, Calcium, and Aluminium in groups 2, 2, and 13 respectively
Hence, we can conclude based on the experimental observation of reactive activity trend for both period and group that Li, Na, and K belong to group 1 and are more reactive than Mg, Ca, and Al across the period.