$\mathrm{y}_{2}=\mathrm{a}_{2} \sin \left(\omega \mathrm{t}-\frac{2 \pi \mathrm{x}}{\lambda}+\frac{\pi}{2}+\phi\right)$
$\Delta \phi=\frac{\pi}{2}+\phi$
So, $\frac{\Delta \phi}{2 \pi}=\frac{\Delta x}{\lambda} \Rightarrow \Delta x=\frac{\lambda}{2 \pi}\left(\frac{\pi}{2}+\phi\right)$
$(A)$ the intensity of the sound heard at the first resonance was more than that at the second resonance
$(B)$ the prongs of the tuning fork were kept in a horizontal plane above the resonance tube
$(C)$ the amplitude of vibration of the ends of the prongs is typically around $1 \mathrm{~cm}$
$(D)$ the length of the air-column at the first resonance was somewhat shorter than $1 / 4$ th of the wavelength of the sound in air