Question

what could be the reason for the change in reactivity of elements​

Answer 1

These react by losing electrons and reactivity increases as you go down the group. This is because the increased number of electron shells results in more shielding and a greater distance between the outer electrons and the nucleus, which reduces the attraction of the electrons to the nucleus

Answer 2

Answer:

during winter ghee and oil get converted to solids. in in winter atmosphere temperature falls the molecules of ghee, oil etc lose their Kinetic energy and comes closer and to each other .hence the liquid changes to solid