Solution:

$F^{-1}[X(j \Omega)]=F^{-1}[\delta(\Omega)]\\ $

$x(t)=\frac{1}{2 \pi} \int_{-\infty}^{\infty} X(j \Omega) e^{j \Omega t} d \Omega\\ $

$=\frac{1}{2 \pi} \int_{-\infty}^{\infty} \delta(\Omega) e^{j \Omega t} d \Omega=\frac{1}{2 \pi}[1]\\ $

$F^{-1}[\delta(\Omega)]=\frac{1}{2 \pi}\\ $