Rohtas produces the most wheat in Bihar — option 3.

Why Rohtas. The district lies in south-western Bihar, in the plain watered by the Sone canal system — one of the oldest large irrigation works in India, taken off at Dehri-on-Sone from the 1870s. Assured canal irrigation, deep alluvial soil and a cool dry winter give exactly the conditions wheat needs, and the district is called the rice bowl of Bihar for its kharif crop and is equally strong in rabi wheat.

What wheat needs. A cool growing season of 10 to 15 °C with 50 to 75 cm of moisture, and warm dry weather at ripening. It is a rabi crop, and its productivity depends far more on irrigation than on rainfall — which is why the canal districts of Bihar lead, just as Punjab and Haryana lead nationally.

Bihar’s place in wheat. The state is among the larger wheat producers in India, after Uttar Pradesh, Madhya Pradesh, Punjab and Haryana, but its yield per hectare is well below theirs. The reasons are late sowing after paddy, small and fragmented holdings, uneven power supply for tube wells, and limited mechanisation — the same set of constraints that runs through the state’s agriculture generally.

A note on the other districts. Bhojpur and Patna also lie in the Sone and Ganga plains and grow wheat substantially, so the question turns on a district ranking rather than on any general principle; Jahanabad is much the smallest of the four.

Hence, the answer is Rohtas.