The structure that corresponds to the most stable conformation of the following compound is

Concept:

• In a 6-membered heterocyclic system, the electronegative group joined with the adjacent carbon of hetero-atom prefers a more sterically hindered axial configuration over a less steric equatorial position.
• The reason behind this is anomeric effect as shown by the picture given below:

• As we can see in axial conformation the antibonding orbital of the adjacent group is parallel to the non-bonding orbitals of oxygen. The lone pairs can be shared to the antibonding orbital, providing them extra stability. This is called Anomeric effect.
• No such effect can be seen in equatorial configuration.

Explanation:

The given structure is: 

As we can see two of the chlorine groups on the either left or right side of O are trans to each other. Therefore, option (2) and (3) are incorrect.

Now, the possible configurations are :

and

considering the arrangement of Cl and anomeric  effect the correct and more stable configuration will be the with axial C-Cl bonds, that is:

Conclusion:

Hence, the correct option is (4).