The correct answer is option 1. The balanced reaction represents that a bond is broken and energy is absorbed. Cl2 are held by covalent bonds that are strong. Therefore, energy is required to break these bonds. The energy supplied is absorbed for the reaction to proceed.
In 1917, Rutherford discovered something new, he bombarded alpha particles on nitrogen gas and noticed that occasionally an oxygen atom is produced. From this he concluded that the alpha particles removes proton from the nucleus (positively charged particle). He named this playing with marbles and he become the first one to split an atom. Thus, by bombarding nitrogen with alpha particles, he observed the production of oxygen, a different element.
Therefore, he said bombarding atoms with particles is similar to playing with marbles.
If you only want to balance nuclear reactions, then you should know that number of nucleons are conserved before and after nuclear reaction. Also, charge is conserved as well.
Other things which are conserved in a nuclear reaction are:
Conservation of:
1. Parity
2. Spin
3. angular momentum(vector sum of intrinsic spin and orbital angular momentum)
4. linear momentum
5. Isotopic spin
6. Energy
