Explanation

Acidified potassium permanganate (KMnO4), acidified potassium dichromate (K2Cr2O7), and silver nitrate (AgNO3 (in the form of Tollens' reagent) can all oxidize aldehydes to carboxylic acids. 

Acidified KMnO4:

• A strong oxidizing agent that readily converts aldehydes to carboxylic acids.
• It changes color from purple to colorless during the reaction. 

Acidified K2Cr2O7:

• Also a strong oxidizing agent that can oxidize aldehydes to carboxylic acids.
• It changes color from orange to green during the reaction. 

AgNO3 (in Tollens' reagent):

• A milder oxidizing agent compared to the previous two, but still capable of oxidizing aldehydes.
• It gives a characteristic silver mirror precipitate when reacting with an aldehyde.