Match List - I with List - II.

	List-I		List-II
(a)	Aspergillus niger	(i)	Acetic Acid
(b)	Acetobacter aceti	(ii)	Lactic Acid
(c)	Clostridium butylicum	(iii)	Citric Acid
(d)	Lactobacillus	(iv)	Butyric Acid

The correct option is a-(iii), b-(i), c-(iv), d-(ii).

To match List-I (microorganisms) with List-II (organic acids produced by them), we can analyze each pairing based on industrial microbiology concepts:

1. (a) Aspergillus niger: This is a filamentous fungus widely used in biotechnology for the production of Citric Acid. Therefore, (a) matches with (iii).

2. (b) Acetobacter aceti: As the name suggests, this bacterium is responsible for converting ethanol into acetic acid (vinegar). Therefore, (b) matches with (i).

3. (c) Clostridium butylicum: This anaerobic bacterium fermentatively produces butyric acid (as well as solvents like butanol and acetone). Therefore, (c) matches with (iv).

4. (d) Lactobacillus: This group of bacteria ferments sugars into lactic acid, commonly used in dairy fermentation (like yogurt production). Therefore, (d) matches with (ii).

Summarizing the matches:
• (a) → (iii)
• (b) → (i)
• (c) → (iv)
• (d) → (ii)