$\text{When A=∅, then number of elements in P(A) is}$

$$\begin{gathered} \text{A=∅} \\ \text{n(A)=0} \\ {\text{number of subsets of any set containing 'n' elements is 2}}^n \\ Here n=0, \\ Number of subsets =2^0=1 \end{gathered}$$