Question

The metals of group1 in decreasing order of reactivity is:
A. $Cs > Na > K > Li$
B. $K > Cs > Na > Li$
C. $Cs > K > Na > Li$
D. $Li > Na > K > Cs$

Answer 1

Hint: It is seen that on moving down the group on periodic table, the size increases and ionization energy decreases. Also, it is observed that on moving down the group in alkali metals, the screening effect of inner filled shells on valence s-electron increases.

Complete step by step solution:
We know that metals of group 1 are also known as alkali metals. They are s block elements because the last electron enters in s orbital in them.
The general electronic configuration of alkali metal is $n{s^1}$ where n=2-7.
It has been seen that the chemical reactivity of alkali metals increases on going down the group on periodic table.
This happens because as we go down the group on periodic table, more electron shells are added to the atoms due to which the atomic radii of successive elements keep on increasing.
With each extra electron shell, the outermost electrons or valence electrons become further away from the nucleus and the force of attraction binding them to the nucleus keeps on decreasing.
As a consequence, it becomes easier for these outermost electrons to escape from the atoms and makes the atom more reactive.
This is the reason why metal reactivity increases on going down the group.
From the above discussion we can say that in case of metals of group 1, the order of reactivity is: $Cs > K > Na > Li$.
Therefore, we can easily conclude that option C is the correct option.

Note: It should be remembered that on moving down the group on periodic table, both ionization energy and electronegativity of elements tend to decrease whereas metallic character tends to increase on moving down the group on periodic table.