In nuclear fission reactions, what causes the atom's nucleus to become unstable?
A. Control rods being inserted into the nucleus
B. Extreme temperatures released by fuel rods
O C. The absorption of a free-moving neutron by the atom's nucleus
O D. The nucleus absorbing freely moving protons

answer: you could do some invislibe ink.

explanation: i will tell you how to if u answer my question.

explanation:

let the different atoms be x and y. each with four protons and same mass will be represented as follows.

mass number is number of protons + number of neutrons.

            and  

since, it is given that one has a negative charge while the other is neutral. therefore, there will be increase in number of protons and the atom will be represented as follows.

according to periodic table, mass number of beryllium is 9 and it has atomic number 4 so, the atoms will be and .  

the protons and neutrons will be located inside the nucleus whereas the electrons will be revolving around the nucleus.