Which scenario would cause a covalent bond to form?

Searching for this question, I found the options on the internet.
"1.Two atoms share electrons so they can fill their outer shells2.The constant motion of electrons and the creation of charge imbalances bonds two molecules together3.A hydrogen atom with a slight positive charge is attracted to a negative charge of another molecule or atom4.One atom loses one or more electrons and the other atom gains one or more electrons"

The correct answer would be number 1. A covalent bond is achieved when two atoms share electrons from their outer shell so that they have a full outer shell leading to the electronic configuration balance they need.

Copper, silver, aluminum, cobalt, chromium, mercury 

Answer : option a) 84explanation :

considering the question as per the attachment

here we can see that the radon nuclide has 222 as the atomic mass number and 86 as the atomic number.

when it undergoes nuclear fission it gives polonium which has atomic mass number as 218 and atomic number will be 84 along with a helium nucleus which has 4 atomic mass number and 2 as its atomic number.

222 = 218 + 4 (atomic mass number)

86 = ? + 2; therefore ? = 86-2 = 84.

the atomic mass number of polonium will be 84.