_Na+ Cl2 - -> _NaCl

A 2,4
B 1,2
C 3,3
D 2,2

D 2,2

Explanation:

We can see that there are 2 chlorines on the reactant side so there has to be a 2 on the product side

Now we have Na + Cl2 --> 2NaCl

The problem now is that there are 2 sodiums on the product side so add a 2 to the Na on the reactant side

2Na + Cl2 --> 2NaCl

Now it's balanced!

the seeing the electronic configuration we can say that the element is fluorine.

fluorine is the most electronegative element in the periodic table.

but by only seeing the configuration we cannot say about its reactivity because we don't know if its configuration after excitation or by addition of electrons.

but if not then, it is the lightest halogen and exists as a highly toxic pale yellow diatomic gas at standard conditions. as the most electronegative element, it is extremely reactive: almost all other elements, including some noble gases, form compounds with fluorine.