Based on the first law of thermodynamics,which one of the following is correct?

The mathematical equation of the first law of thermodynamics for an isochoric process is:

The volume of an ideal gas contracts from $10.0 \ L$ to $2.0 \ L$ under an applied pressure of $2.0 \ atm$. During contraction,the system also evolved $900 \ J$ of heat. The change in internal energy (in $J$) involved in the system is $(1 \ L \ atm = 101.3 \ J)$:

An ideal gas is subjected to a cyclic process involving four thermodynamic states. The amounts of heat $(Q)$ and work $(W)$ involved in each of these processes are:
$Q_1 = 6000 \, J, Q_2 = -5500 \, J, Q_3 = -3000 \, J, Q_4 = 3500 \, J$
$W_1 = 2500 \, J, W_2 = -1000 \, J, W_3 = -1200 \, J, W_4 = x \, J$
The ratio of the net work done by the gas to the total heat absorbed by the gas is $\eta$. The values of $|x|$ and $\eta$ respectively are:

In an isothermal expansion,the increase in volume with a decrease in pressure of a gas is greater than in an adiabatic expansion,because .............

Calculate the difference between $\Delta H$ and $\Delta U$ for the combustion of $n$-octane at $25^{\circ}C$. (in $kJ$)