Answer:
Option 1
Explanation:
Option number 1 is the most compact one which indicates it is a solid
I think it is gauche.
I know the angle between two atoms in equatorial positions is 60 degrees. and 60 degrees is seen in gauche conformations.
To do this problem it is necessary to take into account that the heat given by the unknown substance is equal to the heat absorbed by the water, but considering the correct sign:

Clearing the specific heat of the unknown substance:
