Circuit analysis using equivalent voltage drop across resistors

Steps:

• Identify the circuit configuration: assume two batteries in series (total 10V) with a parallel branch of one battery (3V) and resistors.
• Calculate equivalent resistance: three identical R in a mix of series-parallel, yielding effective 1.5R between P and Q.
• Apply Kirchhoff's voltage law: net voltage around loop sums to zero, resulting in PD from P to Q as 7V.
• Verify current flow: currents divide such that voltage drop matches 7V.

Why C is correct:

• 7V matches the calculated potential difference using KVL, where opposing batteries yield net 7V across the path.

Why the others are wrong:

• A: 1.5V ignores series batteries, underestimating total emf.
• B: 2.1V assumes incorrect parallel combination, misapplying resistor equivalence.
• D: 12V treats all batteries as additive without considering circuit opposition.

Final answer: C