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# How many elements has $P(A)$,if $A=\phi$?

$\begin{array}{1 1}(A)\;1&(B)\;2\\(C)\;3&(D)\;4\end{array}$

If $A=\phi$,then by the definition of power set we have
$P(A)=P(\phi)=\{\phi\}$
$\Rightarrow$ a set containing 1 element.
Hence (A) is the correct answer.