The correct answer is option 3, Nagpur. The mean monthly rainfall diagram provided shows the rainfall distribution pattern of different locations. In this case, the diagram specifically represents the average monthly rainfall for each of the given options.

Option 1, Allahabad, is not the correct answer as the rainfall data for this location is not depicted in the diagram. We cannot determine the rainfall distribution pattern for Allahabad based on the given diagram.

Similarly, option 2, Lucknow, is also not the correct answer. The diagram does not provide any information or data regarding the average monthly rainfall in Lucknow.

Option 4, Vadodara, is also not the correct answer. The diagram does not illustrate the rainfall distribution pattern for Vadodara.

Therefore, the correct answer is option 3, Nagpur, as the diagram represents the mean monthly rainfall for this specific location.