\(\therefore \rho gd =2 \times 10^{5} Pa\)
\(P _{2}=2 \rho gd + P _{0}\)
\(=4 \times 10^{5}+10^{5}=5 \times 10^{5} Pa\)
\(\%\)increase \(=\frac{ P _{2}- P _{1}}{ P _{1}} \times 100\)
\(=\frac{5 \times 10^{5}-3 \times 10^{5}}{3 \times 10^{5}} \times 100=\frac{200}{3} \%\)