Question:

Which one of the following Boolean expressions is a tautology?

Show Hint

Simplify each expression using \(q \vee \sim q = T\) and the distributive laws; only one reduces to a statement that is always true.
Updated On: Nov 5, 2026
  • \((p \vee q) \wedge (\sim p \vee \sim q)\)
  • \((p \vee q) \vee (p \vee \sim q)\)
  • \((p \wedge q) \vee (p \wedge \sim q)\)
  • \((p \vee q) \wedge (p \vee \sim q)\)
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The Correct Option is B

Solution and Explanation

Option (2): \((p \vee q) \vee (p \vee \sim q) = p \vee (q \vee \sim q) = p \vee T = T\), a tautology.
Option (1): \((p \vee q)\wedge(\sim p \vee \sim q)\) is the exclusive-or of \(p, q\); it is false when \(p = q = T\).
Option (3): \((p \wedge q) \vee (p \wedge \sim q) = p \wedge (q \vee \sim q) = p\), not a tautology.
Option (4): \((p \vee q)\wedge(p \vee \sim q) = p \vee (q \wedge \sim q) = p\), not a tautology.
Answer: (2) \((p \vee q) \vee (p \vee \sim q)\)
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