The Dandi March was a nonviolent protest led by Mahatma Gandhi in 1930 in colonial India against the British salt monopoly. The participants marched 241 miles to the Arabian Sea coastline, where they made their own salt by evaporating seawater. Hence, the event is associated with `Sodium Chloride`, which is the chemical name for salt.

Let`s look at the other options:

Option 1, `Iron`, is an element that is used in making steel and other alloys. It was not related to the Dandi March.

Option 3, `Sulphur` is an element used in making fertilizer, and it too has no association with the Dandi March.

Option 4, `Aluminium` is a light, strong, and corrosion-resistant metal. It is also irrelevant to the event.

In conclusion, the correct answer is Sodium Chloride because it is synonymous with the main facet of the Dandi March - the production of salt as a symbol of resistance against the British salt monopoly.