Describe the principle of an atom bomb. What is the criticalmass of `._(92)U^(235)` ?

Explanation

### Step-by-Step Solution:

**Step 1: Understanding Nuclear Fission**
- Nuclear fission is the process in which the nucleus of an atom splits into two or more smaller nuclei, along with the release of energy. This process can occur spontaneously or can be induced by bombarding the nucleus with neutrons.

**Step 2: Principle of an Atom Bomb**
- An atom bomb operates on the principle of uncontrolled nuclear fission chain reactions. In this process, a fissile material, such as Uranium-235 (U-235) or Plutonium-239 (Pu-239), undergoes fission when it absorbs a neutron.

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