In the circuit shown, what is the potential difference V_PQ in volts?

Applying KVL for the 1st loop,

$-2+2{\mathrm{I}}_1-4+1\left({\mathrm{I}}_1\right)=0;$

$3{\mathrm{I}}_1=6\Rightarrow {\mathrm{I}}_1=2\mathrm{A}$

$V_P-V_Q=\left(V_P-V_B\right)+\left(V_B-V_A\right)+\left(V_A-V_Q\right)$

$=-1\left(2\right)+4+0=2\mathrm{V}$

here ${\mathrm{V}}_{\mathrm{PQ}}=\left|{\mathrm{V}}_{\mathrm{P}}-{\mathrm{V}}_{\mathrm{Q}}\right|=\left|{\mathrm{V}}_{\mathrm{Q}}-{\mathrm{V}}_{\mathrm{P}}\right|$

$\therefore \text{ Ans }=2\mathrm{V}$