b
(b) To produce $5$ beats/sec.
Frequency of one wire should be increase up to $505 \,Hz$. i.e. increment of $1\%$ in basic frequency.
$n \propto \sqrt T $ or $T \propto {n^2}$
==> $\frac{{\Delta T}}{T} = 2\frac{{\Delta n}}{n}$
==> percentage change in Tension =$2\,(1\% ) = 2\% $