Kirchhoff's Laws & Measuring Instruments question from NEET 2019

Answer: (a)

1. Take the left node at $2\text{ V}$ and the right node at $0$. Each branch has $50\ \Omega$, an ideal voltmeter draws no current.
2. Top branch: middle point $= 2 - 2 \times \dfrac{20}{50} = 1.2\text{ V}$.
3. Bottom branch: middle point $= 2 - 2 \times \dfrac{30}{50} = 0.8\text{ V}$.
4. Reading $= 1.2 - 0.8 = 0.4\text{ V}$
5. So the answer is (a) $0.4\text{ V}$.