Step 1: What the question asks:
We need the reason that makes a group a counter movement. The test is simple: it must push back against a reform and protect the old custom.
Step 2: Identify the reform:
The reform in question is the ban on Sati, pushed by social reformers and the colonial state.
Step 3: Locate Dharma Sabha:
Dharma Sabha was formed by orthodox Hindus who objected to the ban and wanted the custom to continue as before.
Step 4: Match to the options:
Option 2 says it defended Sati and refused any change. This matches. Option 3 and option 4 both have the group supporting an end to Sati in some way, which is against the facts. Option 1 narrows the matter to older women, which is not what the dispute was about.
Step 5: Result:
Option 2 gives the true reason.
Cross-check:
A quick way to remember the idea is to pair each side with its action. Reformers such as Raja Rammohun Roy asked for a ban on Sati, and the state passed it in 1829. Dharma Sabha answered by petitioning against the ban and defending the custom. When one group pushes for change and another group is built only to stop that change, the second group is called a counter movement. This clear pairing supports option 2.
Final Answer:
Option 2 is correct.
\[\boxed{\text{Option 2}}\]