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From Wolfram MathWorld:

A statement is in conjunctive normal form if it is a conjunction (sequence of ANDs) consisting of one or more conjuncts, each of which is a disjunction (OR) of one or more literals (i.e., statement letters and negations of statement letters; Mendelson 1997, p. 30).

A 2-CNF formula is a CNF formula such that every clause has at most two literals.

Is it true that every CNF formula have an equivalent 2-CNF formula? How do you dis/prove this statement?

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    If $x\lor y\lor z$ is logically equivalent to $A_1\land A_2\land\dots\land A_n,$ then $x\lor y\lor z$ logically implies $A_1.$ Now, how could $x\lor y\lor z$ imply a formula $A$ which is a disjunction of two literals? We could simply assign values to the variables occuring in $A$ in such a way as to falsify $A,$ and then assign "true" to whichever of the variables $x,y,z$ does not occur in $A.$ – 2017-02-01

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