(A) The condition for significant diffraction is that the size of the obstacle or aperture $(d)$ must be comparable to the wavelength $(\lambda)$ of the wave, i.e., $\frac{\lambda}{d} \approx 1$.
For visible light, the wavelength $\lambda$ is approximately $6 \times 10^{-7} \,m$. Since most obstacles in our daily life are much larger than this (e.g., $d \approx 10^{-1} \,m$ to $1 \,m$), the ratio $\frac{\lambda}{d}$ is extremely small, making diffraction negligible.
For sound waves, the audible frequency range is $20 \,Hz$ to $20,000 \,Hz$. Taking a typical frequency of $332 \,Hz$ and the speed of sound $v = 332 \,m/s$, the wavelength is $\lambda = \frac{v}{f} = \frac{332}{332} = 1 \,m$.
Since the wavelength of sound $(1 \,m)$ is comparable to the size of common obstacles like doors or windows, the ratio $\frac{\lambda}{d}$ is significant, leading to prominent diffraction.
Therefore, we can hear sounds around corners or through doorways, but we cannot see light around them.