When we go down the Group 1 or the alkali metals group, the elements we observe in order are Li, Na, K, Rb, Cs. As we go down the group, metallic character increases.

Metallic character of something can be expressed as the reluctance to lose electrons. A molecule is said to be more metallic than the other if it loses an electron more easily than the other.

Now, an atom will lose an electron more easily if the nuclear attraction on the electrons of valence shells would be as low as possible to facilitate the loss.

As we go down a group in a periodic table, electrons get added to the last shells. As a result of which the elements which are situated at the bottom of a group do not feel the nuclear attraction which the elements at the top of the group feel. This is because in the elements at the bottom of a group, we see that the valence electrons are very far from the nucleus, due to which the nuclear attraction that these electrons receive is quite negligible. So, these electrons can be removed very easily and the formation of cations is preferred. Therefore, these metals are said to be more metallic than the ones at the top of the group.

So the metallic order is as follows:-

LiH < NaH < KH < RbH < CsH