Which of the following is not a state function?

$A$ thermos flask containing some ice cubes is sealed tightly. This is an example of which type of system?

Enthalpy change for freezing of $1 \ g$ of water at $1 \ bar$ and $0^{\circ} C$ is $334 \ J$. Calculate the internal energy change in $J$ when $1 \ g$ of water is converted into ice?

Which one of the following reactions has $\Delta H = \Delta U$?

Two moles of an ideal gas is expanded isothermally and reversibly at $300 \ K$ from $1 \ L$ to $10 \ L$. The enthalpy change in $kJ$ is

Which of the following symbols represents the heat of reaction at constant volume?