# What height would a water barometer need to be to measure atmospheric pressure?

$\begin{array}{1 1}(A)\;\text{8.743m of mercury}\\(B)\;\text{30.75m of }H_2O\\(C)\;\text{40.8m of }H_2O\\(D)\;\text{10.19m of }H_2O\end{array}$

$P_{atm}\approx 1bar=1\times 10^5N/m^2$
$10^5=\rho gh$
$\Rightarrow h=\large\frac{10^5}{1000\times 9.81}$$=10.19m of water. Or h=\large\frac{10^5}{13.6\times 10^3\times 9.81}$$=0.75m$ of mercury.
Hence (D) is the correct answer.