The volume occupied by the molecules contained in $4.5\text{kg}$ water at STP, if the intermolecular forces vanish away is:

If intermolecular forces vanish, water behaves as an ideal gas. At STP, $1\text{mole}$ of gas occupies $22.4\text{L}$.Molecular mass of water ($H_{2}O$) $=18\text{g/mol}$.Mass of water $=4.5\text{kg}=4500\text{g}$.Number of moles $n=\frac{4500}{18}=250\text{moles}$.Volume $V=250\times 22.4\text{L}=5600\text{L}$.Converting to ${\text{m}}^3$:
$$V=5600\times 10^{-3}{\text{m}}^3=5.6{\text{m}}^3$$