Two identical p-n junctions may be connected in series with a battery in three ways figure. The potential difference across the two p-n junctions are equal in

Circuit 1: The first p-n junction is forward biased since the p-side is at greater potential than the n-side. Also, the second p-n junction is reverse biased since its p-side is at lower potential than its n-side. Therefore, the potential across the first (forward biased) and the second (reverse biased) p-n junction is not equal.

Circuit 2: The first p-n junction is forward biased since the p-side is at greater potential than the n-side. Also, the second p-n junction is forward biased since its n side is at lower potential than its p side. Therefore, the potential across the first and the second p-n junction (both forward biased) is same.

Circuit 3: The first p-n junction is reverse biased since the n-side is at greater potential than the p-side. Also, the second p-n junction is reverse biased since its p-side is at lower potential than its n-side. Therefore, the potential across the first and the second p-n junction (both reverse biased) is same.

Therefore, the correct answer is option B.