Answer the following in one or two words.

The chemical reaction that involves addition of hydrogen or removal of oxygen.

When hydrogen is passed over a black solid compound ‘$\mathrm{A}$’, the products are a colourless liquid and a reddish brown metal ‘$\mathrm{B}$’ The substance ‘$\mathrm{B}$’ is divided into two parts and each part is placed in separate test tubes. To one part of the substance ‘$\mathrm{B}$’ dil. $\mathrm{HCI}$ is added and to the other part dil. ${\mathrm{HNO}}_3$ is added.

What happens to substance ‘A’ when it reacts with hydrogen? Give reasons for your answer.

In the following reactions name the substance oxidised, the substance reduced, an oxidising agent and a reducing agent.

${\mathrm{Fe}}_3{\mathrm{O}}_4+4{\mathrm{H}}_2\to 3\mathrm{Fe}+4{\mathrm{H}}_2\mathrm{O}$

When hydrogen is passed over a black solid compound ‘$\mathrm{A}$’, the products are a colourless liquid and a reddish brown metal ‘$\mathrm{B}$’ The substance ‘$\mathrm{B}$’ is divided into two parts and each part is placed in separate test tubes. To one part of the substance ‘$\mathrm{B}$’ dil. $\mathrm{HCI}$ is added and to the other part dil. ${\mathrm{HNO}}_3$ is added.

Name substances ‘$\mathrm{A}$’ and ‘$\mathrm{B}$’

What is a reducing agent? Is hydrogen a reducing agent?

$\mathrm{CuO}+{\mathrm{H}}_{2 }\to \mathrm{Cu}+{\mathrm{H}}_2\mathrm{O}$

Write the reaction that is carried out when $\mathrm{Zn}\left(\mathrm{II}\right)\mathrm{oxide}$ is reduced to $\mathrm{Zn}$ using a reducing agent carbon.  

In the following reactions, name the substance oxidised, the substance reduced, an oxidising agent, and a reducing agent.

Hydrogen is used in the _____of metals.