Explanation:

Correct answer is (c). 

If we read the two given statements carefully, we can infer that both are contradictory in nature.
Applying the elimination technique, let’s check the relevance of each of the options one by one.
Possibility 1.
With a view to ratifying the UN Convention against torture and other cruel, inhuman or degrading treatment or punishment treaty, India signed it two decades ago.
Though the connector ‘With a view to ratifying …..’ goes well with the statement I yet it doesn’t keep the context intact and implies a different meaning from what is inferred from the given statements.
Options B and D hence can be eliminated.
Possibility 2.
Two decades after signing the UN Convention against Torture and Other Cruel, Inhuman or Degrading Treatment or Punishment treaty, India is yet to ratify it.
Clearly, the above synthesis is both grammatically and contextually correct and keeps the flow intact.
This eliminates option A as well.
Possibility 3.
Despite signing the UN Convention against Torture and Other Cruel, Inhuman or Degrading Treatment or Punishment treaty two decades ago, India is yet to ratify it.
This construction is also correct as it states the same context as described in the given statements.
Option C is hence the correct answer.