Define thermal conductivity. Also,provide its $SI$ unit and dimensional formula.

(N/A) Thermal conductivity $(k)$ is defined as the rate of heat transfer through a unit thickness of a material per unit area per unit temperature difference.
It is given by the formula: $Q = \frac{kA(T_1 - T_2)t}{d}$,where $Q$ is the heat transferred,$A$ is the area,$d$ is the thickness,and $(T_1 - T_2)$ is the temperature difference.
Rearranging for $k$: $k = \frac{Qd}{A(T_1 - T_2)t}$.
$SI$ Unit: The unit of heat is Joule $(J)$,area is $m^2$,thickness is $m$,temperature is Kelvin $(K)$,and time is second $(s)$. Thus,the unit is $\frac{J \cdot m}{m^2 \cdot K \cdot s} = W \cdot m^{-1} \cdot K^{-1}$.
Dimensional Formula: Since $Q$ is energy $([ML^2T^{-2}])$,$d$ is length $([L])$,$A$ is area $([L^2])$,$\Delta T$ is temperature $([K])$,and $t$ is time $([T])$:
$k = \frac{[ML^2T^{-2}][L]}{[L^2][K][T]} = [MLT^{-3}K^{-1}]$.