Concept:
Eco-friendly bleaching agents are preferred because they do not produce toxic by-products.
Step 1:
Hydrogen peroxide acts as oxidizing bleaching agent.
\[
H_{2}O_{2}
\]
Step 2:
It decomposes into:
\[
H_{2}O + O_{2}
\]
which are non-polluting.
Step 3:
• Tetra chloroethane is toxic
• Acetanilide is a medicinal compound
• Acetone is a solvent
Step 4:
Hence environmentally safe bleaching agent is:
\[
\boxed{H_{2}O_{2}}
\]
\[
\boxed{\text{Correct Option = (3)}}
\]