Q87 / 180 · KCET 2010 · Mathematics
In $P(X)$, the power set of a non-empty set $X$, an binary operation * is defined by $\mathrm{A}{ }^{*} \mathrm{~B}=\mathrm{A} \cup \mathrm{B}, \forall \mathrm{A}, \mathrm{B} \in \mathrm{P}(\mathrm{x})$ under $*$, a true statement is
- Aidentity law is not satisfied
- Correct answerBinverse law is not satisfied
- Ccommutative law is not satisfied
- Dassociative law is not satisfied
Solution
Under the binary operation,
$\mathrm{A} * \mathrm{~B}=\mathrm{A} \cup \mathrm{B}, \forall \mathrm{A}, \mathrm{B} \in \mathrm{P}(\mathrm{x})=$ Power set
Inverse of 'A' does not exists because
$$
A * B \neq \phi \text {, for any } B \in P(x)
$$
Where $\phi$ is the identity element in $P(x)$.
While under the binary operation $A * B=A \cup B$, the commutative law, associative law and identity elements are exists.
Hence, the correct answer is option: 'B'.