• Standard Single Super Phosphate (SSP) contains $16\%$ available phosphorus ($P_2O_5$), along with $11\%$ sulphur and $19\%$ calcium.
• Formula: $\text{Quantity of SSP} = \frac{\text{Required } P_2O_5}{\%\, P_2O_5 \text{ in SSP}} \times 100$.
• Substituting the given values: $\text{Quantity of SSP} = \frac{80}{16} \times 100 = 5 \times 100 = 500\text{ kg}$.
• Hence, option 3 is the correct answer.

Snails are destructive molluscan pests that feed on seedlings and foliage; they are never used as organic farming inputs.

In contrast, Glomus is a vesicular-arbuscular mycorrhizal (VAM) fungus used for phosphorus uptake, Earthworms are used to produce vermicompost, and Oscillatoria is a nitrogen-fixing cyanobacterium (BGA) biofertilizer.

Complex fertilizers are chemical compounds containing two or more primary plant nutrients ($N, P, K$) synthesized through chemical reactions.

DAP contains 18% Nitrogen and 46% Phosphorus ($P_2O_5$) chemically combined, making it a classic complex fertilizer.

Aspergillus is a fungus primarily utilized as a Phosphate Solubilizing Microorganism (PSM), not as a nitrogen fixer.

In contrast, Azospirillum, Acetobacter, and Azotobacter are well-known biological nitrogen-fixing bacteria.