Light green crystals of ferrous sulphate lose water molecules and turn brown on exposure to air. This is due to its oxidation to:

What is a redox reaction? Explain its uses.

Identify the redox reaction out of the following reactions and identify the oxidising and reducing agents in them.
$(d)$ $PCl_{3(l)} + 3H_2O_{(l)} \to 3HCl_{(aq)} + H_3PO_{3(aq)}$
$(e)$ $4NH_{3(aq)} + 3O_{2(g)} \to 2N_{2(g)} + 6H_2O_{(g)}$

Assign $A, B, C, D$ from the given type of reaction.
$PbCrO_4 \downarrow + 4NaOH \,(Excess) \longrightarrow Na_2[Pb(OH)_4] + Na_2CrO_4$

When an acidic solution of $K_2Cr_2O_7$ is added to $Na_2SO_3$,it turns green. Which of the following compounds is formed in this reaction?

$H_2S$ acts only as a reducing agent while $SO_2$ can act both as a reducing and oxidizing agent because