Introduction:
The National Defence Academy (NDA) exam is conducted by the Union Public Service Commission (UPSC) to select candidates for admission into the Indian Army, Navy, and Air Force. The exam pattern for NDA consists of a written examination followed by an interview process. The conducting authority, UPSC, has the authority to introduce modifications in the NDA exam pattern.

Explanation:
The weightage of marks in the NDA exam can change if the conducting authority introduces any modifications in the exam pattern. Let's understand how this can happen:

1. Changes in the Written Examination:
The written examination of NDA is divided into two sections, Mathematics and General Ability Test (GAT). Each section carries a specific weightage of marks. If UPSC decides to modify the exam pattern by changing the number of questions or the marking scheme in either of these sections, it can lead to a change in the weightage of marks allotted to each section.

2. Introduction of New Subjects or Topics:
UPSC has the authority to introduce new subjects or topics in the NDA exam. If a new subject or topic is added, it may carry a certain weightage of marks. This can change the overall weightage of marks in the exam.

3. Changes in the Interview Process:
Apart from the written examination, the NDA selection process also includes an interview. If UPSC introduces any modifications in the interview process, such as changing the number of rounds, the weightage of marks assigned to the interview can change. This, in turn, can affect the overall weightage of marks in the final selection process.

Conclusion:
In conclusion, the weightage of marks in the NDA exam can change if the conducting authority introduces any modifications in the exam pattern. These changes can be in the form of modifications in the written examination, introduction of new subjects or topics, or changes in the interview process. It is important for candidates to stay updated with any modifications introduced by UPSC to prepare effectively for the NDA exam.