The combination of gates shown below is equivalent to which of the following gates?

The boolean expression of this arrangement is,

For NOT gate

$\mathrm{P}=\overline{\mathrm{A}},\mathrm{Q}=\overline{\mathrm{B}}$

For NOR gate

$\mathrm{R}=\overline{\overline{\mathrm{A}}+\overline{\mathrm{B}}}$

For NOT gate G₄

$\begin{array}{r}\mathrm{Y}=\overline{\mathrm{R}}\\ \mathrm{Y}=\overline{\overline{\overline{\mathrm{A}}+\overline{\mathrm{B}}}}\\ \mathrm{Y}=\overline{\mathrm{A}\cdot \mathrm{B}}\end{array}$

Truth Table