Find the current drawn from the battery and the potential difference between B and C.
2 A, 4 V
Equivalent resistance, Req= (2 || 2) + 1 + 1 + (4 || 4) = 1 + 1 + 1 + 2 = 5 Ω
So current in the circuit, I = VReq = 10 V5 Ω = 2 A
Now voltage across BC, VBC = IRBC = 2 A ×(1+1) Ω = 4 V