How literal is this phrase?

Sample examples at http://tinyurl.com/is-it-lit

chain reaction:

Definitions:

  1. a series of chemical reactions in which the product of one is a reactant in the next
  2. a self-sustaining nuclear reaction; a series of nuclear fissions in which neutrons released by splitting one atom leads to the splitting of others

Examples:

  1. more modern methods are used to amplify portions of DNA , typified by the polymerase chain reaction ( PCR ) . The use of DNA sequencing has rendered distance measures such as
  2. In such a tense situation ] even a small little incident can result in a chain reaction which nobody will be able to control . ... [ A major conflict could ]
  3. But the water in those seas would have been cool enough to allow the chemical chain reactions required by " spontaneous animation . " So among Darwinists there arose a broad consensus
  4. can deliver a local election result in London so disastrous for New Labour that a chain reaction will start that will go on to sweep Tony Blair out of 10 Downing Street
  5. coming in . This can be achieved faster by making " combos " ( a chain reaction that removes more than one sequence of colours using a single ball ) , managing

Step 1: Select the definition of chain reaction which occurs most of the times in the above examples. Ignore other definitions.

Definition1 Definition2

Note: Please select the answers below carefully based on the definition which occurs frequently in the examples

Step 2: score of 0-5 for how literal is the use of "chain" in the phrase "chain reaction"
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