\(x = 6\, bps\), which remains the same after loading.
Unknown tuning fork \(F_2\) is loaded so \(n_B\downarrow\)
Hence \(n_A -n_B\downarrow = x \)... \((i)\) \(\rightarrow\) Wrong
\(n_B\downarrow -n_A = x\) ... \((ii)\) \(\rightarrow\) Correct
==> \(n-B = n_A + x = 256 + 6 = 262 Hz.\)