Select the correct location on the. Image Which of these four elements is the most reactive metal?
2
He
10
Ne
18
Ar
36
Kr
54
Xe
85 86
Rn
6
B
Be
12
Mg
20
Ca
38
Sr
17
CI
35
Br
53
16
14
Si
15
P
Na
19
K
37
Rb
34
Se
52
Te
32 33
31
Ga
49
In
81 82
TI
113
Nh
Ge
50
Sn
As
51
Sb
83
B
115
Mc
55 56
84
Cs
87
Fr
Ba
88
Ra
Pb
114
FI
Po
At
116 117 118
Lv
Ts Og

detail is given below.

Explanation:

First of all we will discuss the reactivity trend.

As we move from left to right across the periodic table the number of valance electrons in an atom increase. The atomic size tend to decrease in same period of periodic table because the electrons are added with in the same shell. When the electron are added, at the same time protons are also added in the nucleus. The positive charge is going to increase and this charge is greater in effect than the charge of electrons. This effect lead to the greater nuclear attraction. The electrons are pull towards the nucleus and valance shell get closer to the nucleus. As a result of this greater nuclear attraction atomic radius decreases and ionization energy increases and reactivity decreases.

As we move down the group atomic radii increased with increase of atomic number. The addition of electron in next level cause the atomic radii to increased. The hold of nucleus on valance shell become weaker because of shielding of electrons thus size of atom increased.

As the size of atom increases the ionization energy from top to bottom also  decreases because it becomes easier to remove the electron because of less nuclear attraction and reactivity increases.

In this way rubidium is more reactive than sodium and indium is more reactive than Al.

but when we compare across period sodium is more reactive than Al while Ra is more reactive than In.