Step 1: Look at what is being asked.
Think of the social background of the leaders. They preached equality, but they also came from the groups that gained from the old order. Compare each choice with this fact. We will work it out by sorting the choices one at a time.
Step 2: Working through the choices, part 1.
Rule out the choices that make a false statement of fact. Option 1 says leaders found ending untouchability undesirable. Gandhi's campaigns against untouchability show this is untrue.
Step 3: Working through the choices, part 2.
Education was denied to lower castes in the old order, not to upper castes. This choice turns the truth upside down, so it fails.
Step 4: Working through the choices, part 3.
The national movement was built around the fight against colonial rule. Saying it did not see colonialism as an evil goes against this. This choice fails.
Step 5: Working through the choices, part 4.
Here the leaders are shown as working against lower caste discrimination and also guarding upper caste interests. This is the tension that Dalit thinkers pointed out in the movement. This choice passes the test.
Final Answer:
The contradiction lies in the double position of the leaders, so option 4 is the answer. \[ \boxed{\text{Option 4}} \]