The alternatives justify the answer by looking at two periodic properties: atomic radius and electronegativity.
We are looking for periodic tedencies from left to right, because we are looking at the whole group 1.
The atomic radius is a property that increases from left to right on the periodic table, since the group 1 is to the left, it has a small atomic radius.
The electronegativity is the attraction to electrons of an atom, and it increases from left to right on the periodic table. Thus, the group 1 has low electronegativity, so it is easy for them to lose electrons.
Thus, the correc alternative is "Group 1 metals have a small atomic radius compared to the other elements and can lose electrons easily."