The correct option among the given choices is option 4: Use of superior military technology by the invading army. This means that the use of advanced military technology by Nadir Shah`s army was not a possible reason for the success of his military campaign in Delhi.

Option 1: Weak Mughal Emperor - This explains that one possible reason for Nadir Shah`s success could be the presence of a weak Mughal Emperor, as a strong ruler would have been able to resist the invasion more effectively.

Option 2: Lack of strong defense in the North-West Frontier - This suggests that the absence of a strong defense system in the North-West Frontier region could have contributed to Nadir Shah`s success. A well-established defense could have hindered the invading army`s advancement.

Option 3: Late preparation for the defense of Delhi - This implies that the delay in preparing for the defense of Delhi may have given Nadir Shah an advantage, as the defending forces would not have been fully prepared to face the invasion.

In conclusion, while options 1, 2, and 3 provide possible reasons for the success of Nadir Shah`s military campaign, option 4 is the correct answer as it states that the use of advanced military technology was not a contributing factor.