A 10V battery with internal resistance 1Ω and a 15V battery with internal resistance 0.6Ω are connected in parallel to a voltmeter. The reading in the voltmeter will be close to.

Applying KVL in the circuit
15 - i - 0.6 * i = 0
The current through the voltmeter will be negligible as the voltmeter has very high resistance.
⇒ i = 15 / 1.6 = 25/8 A
The voltmeter reading is given as the potential difference across points A and B
ΔV = -i * 0.6 + 15 = 15 - (25/8) * 0.6 = 15 - 1.875 = 13.125 V
The reading across the voltmeter will be 13.125 V, so the correct option is B.