Out of #Na, Li, K, Fr#, which element has the smallest atomic radius?
Look at the Periodic Table, and you will find all of the listed metals above in the leftmost column as you look at it. These are the alkali metals.
Atomic size decreases ACROSS a Period as we look at it from left to right, but INCREASES down a Group. So given a Table, and there should be one beside you now, you can order the metal atoms with respect to size.