Two statements are given, one is labelled as Assertion (A) and the other as Reason (R):
Assertion (A) Pre-capitalist conquerors in India benefited from their domination by exacting a continuous flow of tribute.
Reason (R) They did not interfere with the economic base of our country.

Both (A) and (R) are true and (R) is not the correct explanation for (A)

The correct answer is Option 2:Both (A) and (R) are true and (R) is not the correct explanation for (A)

Assertion (A) Pre-capitalist conquerors in India benefited from their domination by exacting a continuous flow of tribute. This is is true because pre-capitalist conquerors (like earlier invaders) mainly extracted wealth in the form of tribute, taxes, or gifts, creating a continuous flow of resources.
Reason (R) They did not interfere with the economic base of our country. It is also true because These conquerors generally did not change the economic base (the way people worked, farmed, or traded). The village community remained self-sufficient, and traditional handicrafts continued to thrive. They simply swapped one set of tax collectors for another without forcing the economy to produce different goods or restructuring the land-ownership system for global markets.

Does R Explain A: No. 

• The extraction of tribute (A) is about how they benefited,
• While non-interference in the economic base (R) is about how they ruled, not the reason for tribute extraction.
• The reason they were able to extract tribute was their military and political power, not their lack of interference. One could theoretically interfere with the economic base and still extract tribute (in fact, the British did exactly that through the Land Revenue systems). 

NCERT: "There is a vital difference between the empire building of pre-capitalist times and that of capitalist times. Apart from outright pillage, the pre-capitalist conquerors benefited from their domination by exacting a continuous flow of tribute. On the whole they did not interfere with the economic base. They simply took the tribute that was skimmed off the economic surplus that was produced traditionally in the subjugated areas."