Invalid Boolean Identity

Correct Answer

B — X = X̄

Concept and Reasoning

A Boolean variable and its complement always have opposite logic values, so X is not generally equal to X̄. In contrast, standard Boolean identities include X+1=1, X·X=X and X+0=X. Thus the invalid rule is option B.

Calculation / Key Relation

X+X̄=1

X·X̄=0

therefore X≠X̄

Exam Takeaway

Complement means the opposite Boolean value.

Common Mistake

Do not confuse X=X̄ with the valid complement identities.