Smoke is a colloidal solution where solid particles (such as soot) are dispersed in a gas (air). This is why it is categorized as a solid in gas colloid.
In the system shown below, $x(t)=\sin(t)u(t)$. In steady-state, the response $y(t)$ will be 
The time constant of the network shown in the figure is 
The parallel RLC circuit shown in the figure is in resonance. In this circuit, 