Question

Consider the following balanced oxidation-reduction reaction:

Cl2 + SO2 + 2 H2O --> 2 Cl^1- + SO4^2- + 4 H^1+

Based on the above reaction:
1) Which element is oxidized ?
2) How many electrons are lost by each atom ?
3) Which element is reduced ?
4) How many electrons are gained by each atom ?

Answer 1

For 1 and 3. Loss of electrons is oxidation; gain of electrons is reduction.
But to do this you must know how to assign oxidation numbers to the elements on the left and right. Here is a site that shows you how to do that. Post again if you still have questions but be specific about what you don't understand.
http://www.chemteam.info/Redox/Redox-Rules.html

For 2 and 4. After you learn to do 1 and 3 you will see how to do 2 and 4.