The correct answer is option 'C' - Article 123.

Explanation:
Article 123 of the Indian Constitution grants the President the power to promulgate ordinances during the recess of Parliament. An ordinance is a temporary law that can be issued by the President when Parliament is not in session. The President can promulgate an ordinance if they are satisfied that there are circumstances that require immediate action.

In the year 2002, the Union Cabinet sent the ordinance on electoral reforms to the President for his assent. The President, after examining the ordinance, found that it did not require any changes and gave his assent to it.

Here is a detailed explanation of Article 123 and the process of promulgation of ordinances:

1. Article 123: Article 123 of the Indian Constitution empowers the President to promulgate ordinances during the recess of Parliament. The ordinance has the same force and effect as an Act of Parliament, but it is temporary in nature and requires the approval of both houses of Parliament within a specified period.

2. Power of the President: The President can issue an ordinance if they are satisfied that circumstances exist which render it necessary for them to take immediate action. The President has the power to promulgate an ordinance on any subject on which Parliament has the power to make laws.

3. Approval of the Cabinet: Before promulgating an ordinance, the President must obtain the advice of the Council of Ministers headed by the Prime Minister. The Union Cabinet discusses and approves the ordinance before it is sent to the President for his assent.

4. Assent by the President: Once the ordinance is sent back to the President by the Union Cabinet, the President examines the ordinance and decides whether any changes are required. In the case mentioned in the question, the President found that the ordinance on electoral reforms did not require any changes and gave his assent to it.

5. Approval by Parliament: The ordinance must be laid before both houses of Parliament when it reassembles. It ceases to operate if it is not approved by both houses within six weeks from the reassembly. The ordinance also ceases to operate if resolutions disapproving it are passed by both houses.

In conclusion, the President gave his assent to the ordinance on electoral reforms when it was sent back to him by the Union Cabinet without making any changes in the year 2002, under Article 123 of the Indian Constitution.