The correct answer is option 3: 1, 2, and 3.

Let`s dissect each option for a better understanding:

Option 1 states that unlike in the United States, India has not provided for a double system of courts. This means that India does not have separate federal and state courts like there are in the United States. The judiciary in India is a single integrated system that handles both federal and state matters.

Option 2 states that under the Constitution of India, there is a single integrated system of courts for the Union as well as the states. This aligns with what we discussed in option 1. India`s judiciary is a unified system that caters to both federal and state matters.

Option 3 states that the organization of the subordinate judiciary varies slightly from state to state. This means that each state in India may have slight variations in how the lower courts are organized. This could include differences in jurisdiction, administrative setups, or procedures.

To summarize, all three statements in the given question are correct. India does not have a double system of courts like the United States, has a single integrated system for both the Union and states, and the organization of the subordinate judiciary may vary slightly from state to state.