I need to know what is binding energy and how is it equal to the outcome in energy
I'm sure you do. Did you read this http://en.wikipedia.org/wiki/Binding_energy ? What didn't you understand?
In my physics book it says that as the element increase in mass it has more binding energy , but then like heavier elements have lower binding energy like uranium ?
I'm thinking that you might be confusing total binding energy and binding energy per nucleon.
There is a certain binding energy that keeps a nucleus together and that does generally increase with number of nucleons (although there are exceptions and more complicated features to take into account.
However /how much/ binding energy the nucleus has when you add a nucleon will depend on what you start with. Indeed really heavy nuclei start to get /too/ heavy and adding nucleons to e.g. U235 will not increase the total binding energy as much as e.g. Ne20.
This is reflected in what I called the binding energy per nucleon. This is an average of some sort and you take the total binding energy of the nucleus and devide it by the number of nucleons in the nucleus.
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