The gaseous product formed when dilute nitric acid reacts with silver metal in the absence of air is nitrogen dioxide (NO2). The chemical reaction between silver and dilute nitric acid can be represented as follows:

Ag(s) + 2HNO3(dilute) → AgNO3(aq) + H2O(l) + NO2(g)

In this reaction, silver (Ag) metal reacts with nitric acid (HNO3) to form silver nitrate (AgNO3), water (H2O), and nitrogen dioxide (NO2) gas. The nitrogen dioxide gas is released as a brown-colored gas.

It's important to note that the absence of air is crucial in this reaction. If air is present, oxygen from the air can react with nitric oxide (NO) gas, which is an intermediate product formed during the reaction between silver and nitric acid, to form nitrogen dioxide (NO2).