Two batteries, one of emf 18 V and internal resistance 2 Ω, and the other of emf 12 V and internal resistance 1 Ω, are connected as shown. The voltmeter V will record a reading of :

To find the reading on the voltmeter, we first need to determine the net emf and the total internal resistance of the battery combination. When batteries are connected in series, their emfs add up, and their internal resistances also add up. However, the given circuit is not explicitly described as series or parallel, but based on standard practices, we'll consider a series connection for the calculation of total emf and resistance. The total emf $E_{total}=E_1+E_2=18V+12V=30V$. The total internal resistance $R_{total}=R_1+R_2=2\Omega +1\Omega =3\Omega$. The voltmeter reading will be affected by the current drawn through it, but in an ideal scenario, it should measure the voltage across the points it's connected to without drawing significant current. However, without specific details on how the batteries are connected (series or parallel) and how the voltmeter is placed in the circuit, the most straightforward interpretation involves considering the direct addition of voltages if the batteries are in series. But, if we consider the batteries are connected in such a way that the voltmeter measures the difference between the two (which seems more plausible given the options and a common way to use a voltmeter), then the voltmeter would read the difference in emf between the two batteries, which is $18V-12V=6V$. None of the options directly match this simple calculation, suggesting a misunderstanding in the initial setup. Given the options and aiming for a plausible explanation within the constraints of typical electricity problems, if the batteries were in series and we were looking for a voltage drop across a part of the circuit, we'd need more information on the circuit's configuration. However, my initial explanation aimed to clarify basic principles but may not directly apply due to the lack of specific circuit details. The correct approach should involve understanding the circuit's configuration, which isn't fully detailed here. Therefore, my explanation may not directly lead to one of the provided options without further circuit details.