According to the law of conservation of energy that energy can not be destroyed or created from nothing but it can be converted from one form to another.
In a closed system; the amount of heat released by a part of the system is equal to the amount of heat absorbed by other parts of the system.
<em>Q released = Q absorbed.</em>
<u><em>So, the energy liberated from the air or the walls of the container is 50 kJ.</em></u>
Selenium falls in the same column with oxygen therefore it has the same number of valence electrons with oxygen which is 6. It fills the 3d orbital but only 4s and 4p are counted. The electronic configuration is [Ar]3d^10 4s^2.
To find the number of neutrons, you subtract the atomic number from the mass number of element X. So in this case, it'll be 151-44= the number of neutrons.
