Determine the oxidation number of chlorine in CI2 with the steps

 The oxidation number of chlorine in is zero

Explanation:

Oxidation number or oxidation state : It represent the number of electrons lost or gained by the atoms of an element in a compound.

Rules for Oxidation Numbers are :

1.  The oxidation number of a free element is always zero.

2. The oxidation number of a monatomic ion equals the charge of the ion.

3. The oxidation number of  oxygen (O)  in compounds is usually -2.

4. The oxidation number of a Group 17 element in a binary compound is -1.

5. The oxidation number of  Hydrogen (H)  is +1, but it is -1 in when combined with less electronegative elements.

6. The sum of the oxidation numbers of all of the atoms in a neutral compound is zero.

7. The sum of the oxidation numbers in a polyatomic ion is equal to the charge of the ion.

As exists as a free molecule, its oxidation state is zero.

answer: enthalpy

explanation:

for a exothermic reaction, the energy is released i.e. the energy of the products is lower than the energy of the reactants.

= enthaply

= energy of products

= energy of reactants

as , thus comes out to be negative. negative value of enthalpy shows that the reaction is exothermic.