From a Chemistry perspective it is the electron at 1/1800th the mass of a proton or neutron.
In order for a solute to dissolve in a solvent,
the attractive forces between solute particles and the solvent particles must
be stronger than the attractive forces between solute-solute and
solvent-solvent particles. This is important so that the solute will remain in
solution.
The half-life of this radioisotope : 12 hr
<h3>Further explanation
</h3>
The atomic nucleus can experience decay into 2 particles or more due to the instability of its atomic nucleus.
Usually radioactive elements have an unstable atomic nucleus.
General formulas used in decay:

t = duration of decay
t 1/2 = half-life
N₀ = the number of initial radioactive atoms
Nt = the number of radioactive atoms left after decaying during T time
t=48 hr

The half-life :

Answer:
No of neutrons and protons decides mass of the atom. Electrons having negligible
mass are ignored.
Mass of atom
Mass of atom= sum of no of protons(Z) and neutons(N)
=Z+N
For eg:
In hydrogen atom,
Mass of H= Z+N
=1+0
=1 AMU
An element bonds chemically to fill it's outer valence electron shell, when that occurs it becomes stable.