Volume of tank = $ 2 \times 2 \times 1 \hspace{0.1cm}m^3$
$\qquad \qquad = 4 \hspace{0.1cm}m^3$
Now, we know that, $Density(D) = \dfrac{Mass(M)}{Volume(V)}$
∴ Density of water = $997 \hspace{0.1cm}kg/m^3$
& $Volume = 4 \hspace{0.1cm}m^3$
$∴ \text{M = D}\times V$
$\qquad = 997 \times 4 \hspace{0.1cm}kg$
$\qquad = 3988 \hspace{0.1cm}kg$
$\color{Green}{\text{∴ Volume of water in the tank will be }}$= $4 \hspace{0.1cm} m^3 = 4 \times 1000 \hspace{0.1cm}L = \color{Orange}{4000 \hspace{0.1cm}L}$ $\left[ ∵ 1 \hspace{0.1cm} m^3 = 1000 \hspace{0.1cm}L \right]$
$\color{Maroon}{\text{Weight of water in the tank will be}}$ = $\color{blue}{3988 \hspace{0.1cm} kg}$