Which of the following elements never acts as a reducing agent in a chemical reaction?

Which of the following species acts as the strongest oxidising agent?

Identify the reducing agent in the following reaction:
$CH_{4(g)} + 2O_{2(g)} \longrightarrow CO_{2(g)} + 2H_2O_{(l)}$

Which of the following statements correctly defines an oxidising agent?

$A$ solution of sulphur dioxide in water reacts with $H_2S$ precipitating sulphur. Here,sulphur dioxide acts as:

While sulphur dioxide and hydrogen peroxide can act as oxidising as well as reducing agents in their reactions,ozone and nitric acid act only as oxidants. Why?