\(x = 4\, bps\), which is decreasing after loading (i.e. \(x\downarrow\))
also known tuning fork is loaded so \(n_A\downarrow\)
Hence \(n_A\downarrow-n_B = x\downarrow \)... \((i)\) \(\rightarrow\) Correct
\(n_B -n_A\downarrow = x\downarrow\) ... \((ii)\) \(\rightarrow\) Wrong
==>\( n_B = n_A -x = 256 -4 = 252 Hz.\)