When an aqueous solution of AgNO3 is electrolyzed, a gas is observed to form at the anode. The gas is

Oxygen

Explanation:

First, list out all the ions in the aqueous solution:

Ag+, NO3-

H+, OH-

In the anode, the substance lose electrons to undergo oxidation.

From the 4 ions, only OH- can lose electrons to form water and oxygen,

4OH- --->  O2 + 2H2O + 4e-

While others tend to gain electrons to form new substances instead (they undergo reduction).

Oxygen is the gas produced.

gas

explanation:

smoke is the matter of a gas