Which one of the following functions as an automatic stabilizer in the

Which one of the following functions as an automatic stabilizer in the context of fiscal and monetary policies of an economy?

Personal income tax
Reverse repo rate of bank
Open market operation
Bond price
This question was previously asked in
UPSC CAPF – 2021
Personal income tax functions as an automatic stabilizer because tax revenue automatically increases during economic booms (as incomes rise) and decreases during recessions (as incomes fall), helping to moderate the business cycle without requiring explicit policy changes.
Automatic stabilizers are government programs or policies that counteract the business cycle automatically. During an economic downturn, they stimulate the economy by increasing spending or reducing taxes (e.g., unemployment benefits, progressive income tax). During an upturn, they restrain the economy by decreasing spending or increasing taxes.
Reverse repo rate and open market operations are tools of monetary policy used by the central bank, requiring deliberate action (discretionary policy), not automatic adjustment. Bond prices are market outcomes, not policy tools acting as stabilizers. Other examples of automatic stabilizers include corporate profit taxes and welfare benefits.