B. AgNO₃ is the oxidizing agent
Further explanation
Oxidation is an increase/increase in oxidation number, while reduction is a decrease/decrease in oxidation number.
In the redox reaction, it is also known
Reducing agents are substances that experience oxidation
The oxidizer is a substance that is reduced
Reaction
Cu+2AgNO₃ ⇔ 2Ag + Cu(NO₃)₂
Oxidizing reaction :
Cu⇒Cu²⁺+2e⁻ (oxidation number from 0 to +2)
Reducing reaction
2Ag⁺+2e⁻⇒Ag (oxidation number from +1 to 0)
the oxidizing agent ⇒a substance that is reduced , so that is AgNO₃