Mark the correct statement regarding adiabatic process

For adiabatic process, $\mathrm{\Delta }Q=0$

$\mathrm{\Delta }Q=\text{ nC}△\mathrm{T}\Rightarrow \text{ C}=0$

$\mathrm{dU}={\mathrm{nC}}_v\mathrm{dT}$ is valid for all processes.

Free expansion i.e. expansion of gas against vacuum takes place so fast that there is no time for heat exchange to take place between system & surrounding.But it is not adiabatic as work done by the gas is zero .