Hint: 

Kirchhoff’s second law, also known as the Kirchhoff’s voltage law (KVL) states that the sum of all voltages around a closed loop in any circuit must be equal to zero.

Step 1: To find the e.m.f of the circuit

The resultant resistance of circuit is 

$\Rightarrow R_{\mathrm{e}\mathrm{q}}=2.5+2.5+5+25+15$

 $\Rightarrow 50\Omega .$  

The resultant e.m.f of the circuit is given by

$\Rightarrow ϵ={ϵ}_1-{ϵ}_2$

$\Rightarrow 10-5$

$\Rightarrow 5$

In closed loop 

According kirchhoff's Second law

$\Rightarrow$$10-2.5I-5I-2.5I-5-40I=0$

$\Rightarrow$$5-50I=0$

$\Rightarrow$$I=\frac{1}{10}A$

$\Rightarrow$$V_B-V_A=\frac{1}{10}\times 40=4V$

Therefore, the correct answer is D is $4\mathrm{V}$.