Explanation:
It is known that both sodium (Na) and cesium (Cs) are group 1 elements. This group is also known as alkali metal group.
Both Na and Cs has one valence electron but size of cesium is much larger than the size of sodium.
This means that larger is the size of atom farther away will be the valence electron(s) from the nucleus. Hence, there will be very less or no force of attraction between the nucleus and valence shell.
Therefore, it will be much easy for a larger atom to lose its valence electron. So, the atom will become more reactive in nature.
Thus, we can conclude that Cs is more reactive than sodium metal.
