Which law of thermodynamics can be considered as the definition of temperature?

Which of the following is an extensive property?

If $\Delta H$ is the change in enthalpy,$\Delta U$ is the change in internal energy,$N_P$ is the number of moles of products,and $N_r$ is the number of moles of reactants,then which of the following is correct for a gaseous reaction?

What is a $System$ in thermodynamics?

Two moles of an ideal gas expand spontaneously into a vacuum. The work done is ............. $Joule$.

For the following reaction,the relation between $\Delta H$ and $\Delta U$ is:
$2 SO_{2(g)} + O_{2(g)} \rightarrow 2 SO_{3(g)}$