Why does benzene undergo electrophilic substitution reactions easily and nucleophilic substitutions with difficulty?

Why does benzene undergo electrophilic substitution reactions easily and nucleophilic substitutions with difficulty?
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Ans. Due to the presence of an electron cloud containing 6 pi electrons above and below the plane of the ring, benzene is a source of electrons. Consequently, it attracts the electrophiles towards it and repels nucleophiles. As a result, benzene undergoes electrophilic substitution reactions easily and nucleophilic substitution with difficulty.
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Although benzene is highly unsaturated, it does not undergo addition reactions, why?

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