Option 1 states that the Dandi Yatra or Salt March was the first national activity in which women participated in large numbers. This means that women played a significant role in the march.

Option 2 states that Gandhiji allowed women`s participation in the march at the request of Kamaladevi Chattopadhyay. This suggests that Kamaladevi Chattopadhyay had a role in influencing Gandhiji`s decision to include women in the march.

Option 3 states that the march was fully covered by the Western press. This means that the Western media extensively covered the Dandi Yatra or Salt March.

Option 4, which is the correct answer, states that the march began after the failure of the First Round Table Conference in London. This means that the Dandi Yatra or Salt March took place after the unsuccessful negotiations in the Round Table Conference.

The correct option specifies that the Dandi Yatra or Salt March did not begin after the failure of the First Round Table Conference in London.

Overall, options 1, 2, and 3 provide correct information about the Dandi Yatra or Salt March, while option 4 is incorrect.